The humble Pistol was the weapon of choice for most people, even beyond several of the weapons found later in the game. It had the best accuracy, damage, rate of fire and was available from the beginning of the game. With a little tweaking, you could turn it into a good long range killing machine (without bothering to use the Sniper Rifle). The pistol's Marksman ability, at maximum, will also out-shoot Assault Rifles easily - more rounds, more damage, less heat and more accuracy. With the Infiltrator class, specializing in Commando, as well as a Medical Exoskeleton, it can speed up the recharge on Marksman to the point where you can have the skill enabled permanently.
Now combine Pistol's Marksman with the Immunity ability (i.e. as a Soldier or Infiltrator). You can basically stand still right in front of a pack of six enemies who all have guns blazing on you and methodically take them all down one by one before Immunity wears out. This will work on any game difficulty! The only enemies you'll have trouble with are biotics who can knock you down on the floor repeatedly, but there are only a handful of those kinds of enemies in the whole game, and they're trouble for everyone, not just pistol-users.
Shotguns, fullstop. ME1 shotguns do have very tight pellet groupings that grant considerable range. With the right shotgun stats and equipment, you have a nonscoped sniper rifle in your hands. Add to that high force upon hits and the ability to equip shotguns with specialized ammunition that increases impact force even further and the only thing you can't tie down to the ground are Krogan. And those still die fast enough, even on Insanity if you can hit them before they cast Immunity. If they managed to, well, biotics are instant win abilities.
An Adept's skills, when set up properly, lasted longer than it took for them to recharge. On top of that, they could have the ability to make anything in a Stasis field damageable, which normally renders things invincible for the duration in return for it being unable to fight back. This ability works on the final boss.
Adrenaline Rush. Unlike the later games, each power in ME1 had its own cooldown, independent of all the others. What Adrenaline Rush does is reset the cooldowns of all your powers so you can use them again instantly. In the hands of a Vanguard, this essentially amounts to dual-casting Lift, Throw, and Barrier, with a side of Marksman/Carnage for good measure. And by the time all those run out, you'll probably be ready for another Adrenaline Rush. Oh, and since you've got a bio-amp anyway, Vanguards are ideal for using a biotic bonus power like Singularity for even more chaos. And in case you're worried that tech powers were left out of the fun, Garrus also packs Adrenaline Rush for all your rapid-fire-Overload/Sabotage needs. Enjoy.
A simple method to clear any exploration planet's outdoors in even the highest difficulty would be fire on enemies at a distance that is so far, their health bar and name info will not pop up upon being engaged. The AI will bug, holding down their triggers to return fire against you but staying completely still to maintain a range that almost every enemy will have no hope to hit you at anyway. With just about every exploration planet's outdoors being ridiculously open and spacious, this is pretty much always possible to do on all of them against every enemy - just take out any snipers they have first with a sniper rifle (just about the only weapon capable of hitting anything reliably from so far), keep an eye out for any rocket or large energy ball projectiles they might fire to easily dodge by moving to one side, and you can kill everything outdoors on a planet assuredly (if slowly).
Alternatively, you may utilize the Mako similarly. It can actually be hit by enemies at such a range, but can usually quickly run to a safe spot on a regularly completely open exploration planet to wait for its shields to recharge. Get out of the Mako to land killing blows on enemies when they've gotten low to get full XP for your trouble. This'll probably take a while to do as well (especially since the Mako's shields take a damn long while to recharge), but again, the strategy can make it pretty much impossible for stuff outdoors to kill you when pulled off with no requirements to set up.
Soldiers and Infiltrators both could get Master Immunity and a specialization to reduce its recharge time to be identical to its duration. This ability made the player virtually invincible and could be reused as soon as it wore off. It completely negated the need for cover, which is supposed to be a major defensive component. It also negated the benefits of taking defensive bonus talents, which were pretty logical choices for a Soldier if you didn't realize how effective Master Immunity was.
The Spectre Master weapons, gained by amassing a million credits and buying them from the C-Sec/Normandy requisitions officer (and can be done very early on, if you save enough). Every other gun pales in comparison.
The Mako can be this at times, just about every outside fight is meant to be fought from within the Mako, but if you manage to find one that isn't and still got the Mako there? Well then you have what's essentially a sniper rifle with the ability to kill anything meant to be fought from the ground in one shot. Goodbye difficulty! Although this does significantly decrease the XP received from kills, nothing prevents you from damaging enemies down to a sliver of health and then Cherry Tapping an enemy to death- which you could also do with any fight you use the Mako in, allowing you to net more xp than any fight in the Mako was intended to give you.
Mass Effect 2
The Mattock Assault Rifle for the soldier. It deals ungodly damage in Adrenaline Rush note Adrenaline Rush drastically boosts damage while slowing time, and weapon fire rate slows proportionally. While the Mattock has a maximum fire cap, it's at a rather generous 750 RPM, and on top of this, it's not reduced while under Adrenaline Rush., is extremely accurate, and is available from the start of the game.
The M-29 Incisor Sniper Rifle is a DLC weapon that does decent damage when Shepard equips it, and is available from the beginning of the game. Give it to your allies, however, and you can walk through most of the game without firing a shot, especially on Insanity difficulty (and right from the beginning of the game). As this video shows, Zaeed and Garrus will mow down most enemies in three or four shots, while the player can stay behind and play "spectator" as the AI kills everything in the way with massive damage. According to the game coding, squadmates do reduced damage on higher difficulties with most weapons except those obtained through DLC, making the M-29 king of the hill.
Mass Effect 3
Vanguards have become field-wipers thanks to their new ability, Nova. Nova is normally a Death or Glory Attack because it drains your shields to cause a huge biotic explosion. However, the vanguard staple Biotic Charge regenerates shields, up to 100% capacity with the right upgrade. Should a vanguard equip a light enough weapon, the cooldown between the two can be short enough that a skilled player can jump around blasting any enemy in view over and over again until all that's left is a pasty smear on the wall. And have we mentioned that both Biotic Charge and Nova give the player invulnerability during their duration, making a skilled Vanguard all but invincible?
Note that this doesn't extend to multiplayer, where Vanguards (beside the Krogan) are incredibly squishy, not powerful enough to be a viable Glass Cannon and almost unplayably laggy if not hosting. They are very tough to play well and even then there are better classes.
Really, nova or not, Vanguards with maxed out Biotic Charge and a strong shotgun will turn you into Superman. Equipping light weaponry will leave you with a fast enough recharge to practically spam Biotic charge, which both means practically unlimited shields and the ability to reach every enemy on the terrain in a matter of seconds (knocking them down on impact) and making it impossible to corner you.
If the player is hosting, however, a certain trick you can perform when you use the Nova note The game grants about a second of immunity to any form of damage whatsoever, which you can exploit by cancelling the Nova by, for example, rolling to the side or performing a quick melee attack. Provided you don't run into enemies that can instantly kill you or stagger you, you could walk across a field of Cerberus turrets and come out none the worse for wear by abusing this. turns you into an unstoppable killing machine with some practice. Slap a powerful, yet light enough gun on the human Vanguard and you won't need teammates.
Vanguards also have access to the Shockwave ability. These stumble and harm even the toughest of enemies and can be fired around corners or through walls. If you can max it out for range and cooldown a Vanguard becomes almost unstoppable.
Vanguards also have access to the Incendiary Ammo skill, explained below. It's interesting to note that the skill only applies the extra damage to Health and Armor, but the Nova skill above can get a massive damage boost to Shields and Barriers. Vanguards have all their bases covered with game-breaking abilities.
Now that Overload works against both regular shields and biotic barriers, it's surpassed Warp as the go-to anti-defense power. In addition, its later evolutions can make it jump from target to target chain-lightning style, as well as impart a neural shock effect. Put all these together, and you've got multi-target, anti-shields, anti-barrier, and stun, all in one power.
Likewise, the Energy Drain power has also gotten a similar boost. It can't chain like Overload, but simply making it usable against barriers means that no matter whether you're fighting husks, Cerberus, or geth, there's at least one enemy type available to drain from. This is particularly useful for Infiltrators, since they don't get Overload by default, and the main drawback of Tactical Cloak is that your shields do not recharge while it's active. Energy Drain solves both problems, which is why Salarian Infiltrators (who have Energy Drain) are so prominent in multiplayer.
Incendiary Ammo. The final stage of the skill grants a chance of an explosive burst. The damage of the burst is a set amount of damage (roughly 100 points), unlike previous games where the damage was a percentage of the weapon damage. The upshot? Fast-firing weapons trigger this explosive damage more often. With fast-firing, low-damage weapons this skill can effectively boost damage by +200% while adding an area effect. The Particle Rifle is generally the best weapon to use with this skill, as it has a fast fire rate, can be upgraded with cover penetration, has perfect accuracy, and regenerating ammo. The Geth Pulse Rifle is probably a close second.
This game's version of Stasis has the most potential for game breaking yet. Unlike the first two games, enemies under the effects of Stasis can take damage (though too much damage will break the stasis effect). It also acts as a source power for biotic explosions (which means you can follow up with Warp or Throw for massive damage), it ignores shields and barriers (so Phantoms among others are not immune to it), and a Rank 6 evolution lets it create a bubble that will stun any unarmored enemy that walks into it, essentially making it a multi-target trap like Singularity.
Infiltrators in general.
On anything less than Insanity, where the AI becomes smart enough to work around it, Tactical Cloak is this. While the Infiltrator's signature weapon is the sniper rifle, using Tactical Cloak with just about any shotgun, the Carnifex, or the Paladin means you can run around a map free from enemy fire, walk right behind them, shoot them in the back of the head for massive damage, hide behind cover for what might be, depending on your level, 3 seconds and then you can do it all over again.
They benefit from Tactical Cloak's unique cooldown mechanic - should the Tactical Cloak be canceled before it naturally expires, it has a reduced cooldown. You can break cloak early by shooting or using a power, and getting a damage boost from cloak. Normally, you'd want light weapons (which give bonuses to cooldown) to ensure the cooldown for a useful power like Tactical Cloak remains short. However, by breaking cloak immediately after engaging it, you can force its cooldown to be as low as three seconds. This means Infiltrators get an unparalled damage boost to both powers and weapons (most classes only have passive skill trees that benefit one or the other), and can carry the heaviest (and generally most powerful) weapons in the game while still spamming powers freely with Tactical Cloak's damage boosts.
Power combos are nice enough on their own, but what really broke the difficulty in the single-player was when some observant players discovered the ability to chain different types of power combos. Before patches, it was discovered that using Warp to detonate a Tech Burst did not stop it from priming the target for a Biotic Explosion. Patch 1.04 introduced the ability to keep up repeated Tech Bursts and Fire Explosions just by alternating between Overload and Incinerate. Once this was discovered, Atlases, Geth Primes, and Banshees became the only enemies to provide any challenge. All other shielded enemies found themselves being wiped out en masse. This feature is especially kind to the Engineer and Sentinel classes. The former can damage and stunlock everything at a rapid rate while their drone and turret distract enemies or just shoot rockets at them while the latter went from the Jack of All Stats to the Master Of All, especially with Warp Ammo.
Flare, a bonus power unlocked upon completing the Omega DLC. It's a biotic power that triggers a powerful explosion with a huge radius. It has a base radius of 6 meters, roughly twice that of any power other than some of the grenades, and can be evolved up to a potential maximum of 10.8 meters. Meanwhile, it inflicts close to or over 1000 points of damage, much better than other offensive powers like Warp, and it can be used to detonate Biotic effects and even has an evolution for increasing the damage, force, and radius of Biotic Explosions. Although it's got the longest cooldown time of any power to date in single player, Shepard can still pretty easily bring it down to six seconds or less by selecting lightweight weapons and gear and bonus power recharge rate boosts. Doing nothing but heading for cover and casting it multiple times is sufficient to win most encounters, since each casting will inflict heavy damage to all large enemies in the radius and instantly kill all mooks.
Oh, and it sets off pre-existing biotic primers, such as Reave, Warp, Singularity, and a few others. Double explosions FTW!
Surprisingly enough, the humble Concussive Shot. Exclusive to the Soldier class, it was really only useful against barriers and unshielded husks in 2, but its final rank allows it to have the effects of the active ammo power applied to it, allowing it to burn, freeze, disrupt, warp, or pierce armor. Mind you that the Soldier has three different ammo powers just to start, and can pick up the remaining two as bonus powers, allowing them to set up combos of their choice at will. Selecting the right weapons can give the Soldier a maxed-out power recharge rate, allowing you to chain combos and buzz-saw through enemies with little resistance even on Insanity.
The M8-Avenger is the game's starting rifle, and as such is a Jack of All Stats, with no major weaknesses except being unpredictable at long range, and no major strengths other than being very lightweight. The High Velocity Barrel from the Omega DLC turns the Avenger into a death machine as it ignores 90% of armor and punches through cover like it was made of toilet paper. The reason why the HVB is the perfect match for the Avenger is that the HVB adds a weapon's weight by 50%, but the Avenger is so light that with a few upgrades it practically negates the weight penalty, making it an awesome combination for power-spamming classes. This also works with the M7-Lancer.
The Cerberus Ajax Armor (from the Alternate Appearance Pack DLC) is the most powerful armor for soldiers in the game (outside of the Cerberus Nightmare Armor from the Citadel DLC). Not only do you get the Ajax Armor at the beginning of the game, but it has more cumulative benefits than any other suit in the base game (+25% ammo capacity, +10% weapon damage, +10% power damage, +10% shield-regen speed and +25% shields), making Shepard a near-unstoppable tank who can mow through enemies in any difficulty.
The N7 weapons included in the Collector's Edition are all near or at the top of their class, are available from the start of the game, and (with a mod or two) become devastating:
The N7 Crusader Shotgun. It fires a single, accurate, solid slug rather than buckshot. This essentially makes it an unscoped sniper rifle, with comparable stopping power to the single shot sniper rifles...except it's semi-auto.
The N7 Eagle. It's got the accuracy and power of a pistol, and the fire rate of a SMG. Put a scope on it, and you have a full auto Sniper Pistol. Like the Particle Rifle, you can probably take nothing but the Eagle and do just fine. Note that this doesn't apply to multiplayer, where the N7 Eagle is seen as one of the worst guns in the game.
The N7 Valiant sniper rifle. Like the prohibitively expensive Black Widow, it combines a three-shot clip with good stopping power. Unlike the Black Widow, its recoil and reload time are practically nonexistent, making room-clearing a breeze, and it's light enough to keep power recharge high, and cheap enough to upgrade that you'll get it up to level V moments after the first level.
The N7 Hurricane; if you can learn how to handle the prohibitive recoil, it's got more power per shot than any other SMG, and with magazine expansions, can dish out a whole world of pain. It's especially game breaking when employed by the Turian Soldier class in multiplayer with level V heatsink and thermal clip mods. The Turian Soldier's signature skill, Marksman, increases the firing rate and ammo count and decreases the recoil of his guns. In his hands the modified Hurricane becomes a super accurate death machine that never stops firing.
Several of the weapons obtained through DLC packs are ostensibly broken from a damage output standpoint, and most of them can be accessed from the beginning of the game:
At the top of this list should be the Cerberus Harrier, from the Firefight Pack DLC and the multiplayer Rebellion DLC. As of the MP Reckoning expansion, it is the most commonly used weapon in multi-player. Why? It deals great damage, is fully automatic with a high rate of fire, and is only a mid-weight assault rifle. It stands head and shoulders above every other assault rifle, and can be used by a wide variety of classes, save the most power-centric. Its only flaw is a truly horrendous clip size, which can be fixed with a weapon mod.
The Particle Rifle (from the From Ashes DLC) runs on the same "cooldown" system from the original game, but also uses a beam that gets stronger as the trigger is held down. Not only can the weapon be acquired extremely early (by doing Javik's mission right after Mars), but it can also be augmented like the other weapons with mods. A Particle Rifle with a magazine upgrade and extended barrel will have much more ammo than normal, and will chew through enemy defenses easily, even on Insanity difficulty. Even better, if a Soldier class runs the beam's ammo down to 0 and uses Adrenaline Rush, the weapon's reloading animation (which often takes several seconds) is skipped and the ammo will refill again, saving precious seconds in combat.
The Venom Shotgun from the Groundside Resistance Pack DLC is described, even on the ME wiki, as having all the benefits of a heavy weapon from the previous game, minus the ammo issues. With maxed-out upgrades, an extended barrel and incendiary ammo (which is fairly easy to accomplish early on), the Venom becomes a beast that can one-shot Brutes and Phantoms, and take down Geth Primes, Banshees and Atlases (some of the hardest enemies in the game) in three-four shots. Aside from weight issues, it makes any difficulty up to and including Insanity a complete joke.
The N7 Piranha shotgun (also from Groundside Resistance and the Earth multiplayer pack) has very poor accuracy and a small clip size, but with the right stability upgrades it can do monstrous damage with near-perfect accuracy. To put this in perspective, in single-player, the Level I version of the Pirahna is better than the Level X Katana shotgun (which is also acquired near the beginning of the game).
The Krysae Sniper Rifle (from the Firefight Pack and the Rebellion multiplayer pack) might as well have been called the Krysae Rocket Launcher. Though it can't get headshots, the rounds it fires are explosive and operate on a proximity charge, allowing it to blow up groups of targets with one or two shots each, even on Gold difficulty. With a few damage bonuses even boss-type enemies fall prey to the Krysae's wrath. This gun was the reason that Tactical Cloak and Hunter Mode were nerfed in multiplayer, since they both provided too much synergy with it. And even after being nerfed, it's still in widespread use to this day.
The N7 Typhoon is the most obscenely powerful weapon in the series. It has a damage bonus against all types of protections on top of its already considerable base damage. Once it reaches its maximum firing rate, its damage doubles. When used by Shepard or in multiplayer, it's balanced by being extremely heavy and having horrible stability. What breaks the game is that Shepard's squadmates are completely unaffected by weapon weight and have perfect stability no matter what. It is a testament to the power of the Typhoon that even Kaidan and Javik, who need to rely on other squadmates for ammo powers and potentially have no weapon damage bonuses at all, are capable of easily melting the toughest enemies. Ashley's Marksman ability, James' Incendiary Ammo that was mentioned above, or Garrus' extreme weapon damage bonuses break it even more. Some players eventually stopped giving their squadmates Typhoons because the game became too easy.
From the Citadel DLC:
The M-11 Suppressor Pistol (also from the Citadel and Reckoning DLC) might not have the stopping power of other pistols like the Carnifex or Paladin, but it makes up for it with one of the largest head-shot bonuses in the game. If used with the correct mods (the scope and cranial trauma mods are the two best choices) and enough skill, the Suppressor can reliably kill just about anything except for the heaviest of heavy enemies in two shots or LESS. You don't even have to go out of your way to get it - it's handed to you at the beginning of the first mission.
The M-7 Lancer Assault Rifle (also from the Reckoning DLC) combines the recharging ammo of the Particle Rifle with the power and high rate of fire of the Cerberus Harrier, giving you arguably one of the most powerful weapons in the game. And on top of that, it is also one of the lightest assault rifles in the game, so all but the most power dependent of classes can use it without any problem. The only downside is the slightly less than forgiving recoil which can easily be taken care of with a stability mod.
The M-90 Indra (formerly a Pre-Order Bonus) is handed to Shepard by Liara after completing the "Shore Leave" mission. It's basically a full auto sniper rifle that might not have the punch of, say, the Widow, but add-ons and upgrades fix that. Throw in special talents like cloak or the ability to slow down time when aiming and you could take down Harvesters. Unaided.
Even in the vanilla game, there are a few things that stand out as impressively broken. The Javalin sniper rifle has a scope that highlights enemies behind cover, is virtually as powerful as the Widow, and has innate cover penetration. Combine this with Armor Piercing Ammo and a high-level Piercing modification, and the Javalin can pierce multiple consecutive layers of cover and still be lethal. It is entirely possible to kill enemies several rooms away, or from such a huge distance that their A.I routines don't even trigger a response to the multiple heads exploding around them.
As far as squadmates go, Liara is by far the most useful on Insanity. Her Singularity and Stasis powers let her lock down large groups of mooks at once, leaving you to either blast them with a biotic explosion or ignore them in favor of priority targets. Warp is also useful as a general damage-dealer, and with a Paladin she can be entirely reasonable at gunplay as well.
Slam is subject to some... interesting interactions with the physics engine. A properly timed combination of Slam to lift a target, followed instantly by warp as the target begins to rise off the ground will result int them being launched dozens of meters into the air before slamming back down at tremendous velocity. Absolutely no Slam-vulnerability enemy in the game will survive this combo, even on Insanity. Mixing in Overload/Energy Drain to strip shields off priority targets essentially translates to any humanoid opponent dead in a single fast-recharging combination attack. While not much use against larger reaper enemies, missions against Cerberus become a series of 'who can bounce the highest' contests, as only Atlas mechs cannot be Slammed.
Mass Effect 3 - Multiplayer
Multiplayer has its share of incredibly broken classes and skills:
The final MP DLC, Reckoning, all but cements the place of Infiltrators as the most powerful class, in the form of the Alliance Infiltration Unit. The AIU has a unique cloak similar to the Turian Ghost's: its final evolution at rank 6 can give a boost to shotgun damage fired from cloak. Powerful, but not game-breaking. Its true power lies in another ability: Repair Matrix. Repair matrix offers the AIU some general buffs (speed boost, damage reduction, and shield regeneration), and most importantly, a free revive when she would be downed. For literally very other character in the game, going down means you either wait for a teammate to revive you (and risk being executed by an enemy or simply bleeding out in the meanwhile), or using a medi-gel (of which you can bring at most 6 per game). Proper application of Repair Matrix means you will never die, because you'll revive instantly. The kicker? Repair Matrix is a grenade-based power. This means you can freely refill at ammo boxes. Because Repair Matrix can have a duration of roughly 20 seconds, you can simply run from ammo box to ammo box, all under the protection of Repair Matrix, and so completely trivialize damage taken and death.
The Asari Huntress is perhaps the most powerful asari class. They have Tactical Cloak, of course, and Dark Channel, a powerful biotic damage-over-time power (previously only available to Javik in single-player and the N7 Fury in multiplayer). These two powers combine for a devastating ability that eats up foes' health. First, the Huntress's Tactical Cloak was released bugged—it only gave damage boosts to melee attacks and powers, not weapons. Rather than wait for a patch to fix the bug, it was decided that the Huntress would be given a unique Tactical Cloak: her Tactical Cloak can give a 120% bonus to general damage (though that still only applies to powers and melee) as opposed to the 80% of other Infiltrators, with a further 40% boost to biotic powers instead of sniper damage. Second, Dark Channel while decently powerful but not exceptional on its own, gets a damage boost from Tactical Cloak for the entirety of its duration. So while your cloak may break right after you use Dark Channel, it keeps that 120% damage boost until it runs out... and if its current target dies before that duration expires, it'll simply jump to a nearby foe. A Dark Channel cast under cloak is capable of killing a Banshee from full health on Gold difficulty, all while the Huntress is running about targeting other foes.
The Drell Assassin Infiltrator, as yet another example of why Infiltrators are often considered the most powerful class. Drell have excellent passive bonuses to power and weapons damage, with a unique speed boost evolution in another skill tree, making them fast and hard-hitting. As an Infiltrator, he also gets Tactical Cloak. And he gets Recon Mine, which highlights all enemies in a rather large radius, making them visible through smoke and even walls, as well as potentially slowing them and making them more vulnerable to damage. The icing on the cake? You can detonate the mine, dealing massive damage to all enemies in range. Recon Mine is only available on the Drell Assassin and the Volus Engineer, which as a support class offers much less damage potential. Its fortunately balanced by the fact that Drell are Glass Cannons, with low base health and shields.
The Geth Inflitrator toting an N7 Piranha is agreed by many to be the best multiplayer character. The already overpowered Piranha loses its spread thanks to accuracy bonuses, becoming viable at range, and its already high damage is amped up by cloak, hunter mode and (optionally) proximity mine debuffs.
The Geth Trooper Soldier can deal obscene amounts of damage against armor and health using its flamer ability. While the class has no abilities effective against shields, this can be counteracted by equipping it with an anti shield/barrier weapon such as the Acolyte or Reegar shotgun while still maintaining a relatively low cooldown period. To top this all off, the Trooper has 1000 base shield which can be further upgraded using its class ability with damage reduction added on by Fortification. And of course the Trooper has access to Hunter Mode. At the cost of slightly reduced durability, the Trooper can see through walls and deal even more damage from weapon and ability alike. And unlike most "tank" classes, the Trooper still maintains its agility
The Geth Juggernaut, basically a playable version of the Geth Prime, is so big that it can't use cover and moves very slowly (it can't even run), but it has more health and shields at Level 1 than most classes could possibly get at full upgrade, and all of its powers can be evolved to further increase its toughness. It also has a heavy melee that recharges its own shields and, more importantly, immobilizes small-sized enemies, allowing it to Cherry Tap terrors like Phantoms and Dragoons. It's also immune to sync-kill moves, which makes it viable strategy to have a Juggernaut walk up to a Banshee or Atlas, throw a turret or hex shield in front of it, and then heavy-melee the closest enemy while the rest of the squad pour fire on enemies converging on the Juggernaut. This is viable even on Platinum difficulty, where the Juggernaut can stand at an entryway or corridor, and then become a Stone Wall by using the heavy melee, turning the entryway into a chokepoint as the hordes of enemies plug up the bottleneck trying to reach the Juggernaut. If executed properly and not flanked, the Juggernaut can do this pretty much indefinitely to buy the rest of the squad precious time to deal with other threats. There's even a piece of gear (aptly named the Juggernaut Shield) that improves shields and melee damage to further improve survivability. A group of Juggernauts is even more devastating, as they can assist each other by stunning enemies, deploying energy shields as cover and turrets that can restore each other's shields. It's Boring, but Practical, but the Jugg's survivability and usefulness makes the N7 Destroyer pale in comparison.
The N7 Destroyer Soldier is basically Iron Man brought to the Mass Effect universe. The character is in a big suit of powered armor and is quite powerful. Devastator Mode, even after being nerfed, increases weapon damage, rate of fire and magazine capacity in exchange for losing a bit of movement speed. Additionally, with Devastator Mode active, the Destroyer cannot be stunned. That means that all those overpowered Geth attacks that cause you to stumble will still damage you, but your firing won't be interrupted. Secondly, the Destroyer has the Hawk Missile Launcher. It's an auto-firing missile launcher that can be upgraded in a variety of ways. Its only drawback is that it decreases your max shields. That's a small price to pay for a missile launcher that has an unlimited ammo capacity, doesn't need to be manually locked on or fired and stuns most regular enemies. Finally, the Destroyer has Multi-Frag Grenade, which is pretty good when it comes to grenade powers. All that, though? Not the best part. The best part is that apart from enabling Devastator Mode and the Hawk Missile Launcher at the beginning of a match, the Destroyer never has to worry about cooldown. That means that a Destroyer player can equip the heaviest two weapons he or she wants with no penalty whatsoever. It's no wonder why Bioware nerfed the Destroyer.
The N7 Shadow possesses Shadow Strike, a teleporting backstab that synergises with its cloak and lets it zip around the field like a Vanguard. When set up properly it can inflict massive damage (boosted by both melee, cloak and power attack bonuses) without breaking cloak, possibly twice in a row. The class also has the benefit of cloak (handy for objectives and reviving allies) and a cover-piercing shockwave attack that can set up its own tech bursts and be used in combo with Shadow Strike.
The Targeting VI, an item which will augment headshot damage by 25%, 50%, or 100%, depending on the level. If you can consistently get headshots, you can use this in conjunction with a semi-automatic sniper rifle - say, the Raptor or the Viper. Watch yourself score at the top of matches every time.
The Turian Ghost infiltrator class has amazing synergy with assault rifles, with class passives improving stability and a cloak variant that boosts their damage even more than normal damage-specced cloaks. They combine this with the general utility of cloak, a cloak-boosted overload for stunning and shield-stripping, and Stim Packs, which are deployed instantly like grenades and instantly refill shields (temporarily raising them above max) and give a damage bonus. They can get all this power and survivability and still use heavy weapons without penalty by breaking cloak as soon as it deploys.
The Krogan Warlord Sentinel is what Shepard would be if s/he had four testicles and a hammer large enough to kill a small elephant with. He finds the concept of guns and keeping distance from a fight quaint, launching into the fray with a biotically- or electrically-charged hammer that can kill lesser foes in one shot, and demolish bigger ones with a few more. He gains strength from the ludicrous amounts of enemies he can kill, and has tech armour to replace shields. Which probably won't be needed, since he regains shields and health at an ungodly rate. He does have two particular weaknesses: He is still vulnerable to sync-kills, so he shouldn't just run up to a Banshee or an Atlas head on, and must either come from the side or back, or exploit whatever precious little range his hammer gives him. At higher difficulties this can become a Crippling Overspecialization, as enemies will use sync-kills at every opportunity, and the Battlemaster has no long-range powers, but that doesn't mean he can't equip a gun. His other weakness is a complete inability to take cover or dodge, but this can be mitigated by finding big enough things to hide behind. His Mighty Glacier speed (his walking pace is roughly half that of human characters) is offset once he enters the Krogan Rage, which is triggered by killing two or three enemies in melee in a relatively generous period and upgrades your weapon and melee damage output and resistance and movement speed. Considering enemies tend to come in clusters, it's easy to stay in Rage for an entire game, only possibly slipping out due to the time between waves.