These are what we call the 'YMMV items.' Things that some people find in this work. We call them 'your mileage might vary' because not everyone sees these things in the same way. This starts discussions in the trope lists, a thing we don't want. Please use the discussion page if you'd like to discuss any of these items.
Anti-Climax Boss: The final boss, while not the same joke the one in the original games was (which couldn't attack and could be killed before even entering the room it was in), can be taken down in just a few hits if you bring enough snipers. Woe betide the player who incautiously moves their troops into Rift range and fails to kill him, though - he (and his goons) are more than capable of dishing out a Total Party Kill if you let him.
One sniper with Squadsight and Double Tap armed with a Plasma Sniper Rifle can take the final boss out in a single turn, before the battle can even begin.
You can also ghost in some Heavies and rocket-spam him. He can't handle more than two rockets anyway.
An apparent bug can also cause this, skipping the opening speech of the final boss and causing his underlings not to spawn.
Author's Saving Throw: While the game itself isn't this for 2K, since Enemy Unknown was started before the FPS was announced, looks like Enemy Within is this for The Bureau. Just when people saw the final game and got angry, Enemy Within was announced and that rage was lessened, since the trailers were really promising.
Council Missions once you get far enough into the game. You can be losing good soldiers to Sectopods and Ethereals left and right, and then you're asked to clear a map of Thin Men who were only a challenge back when you couldn't One-Hit Kill them. Those missions are also great for training rookies, as their inexperience is not too much of an issue there. They also make for excellent opportunities to fill in your interrogations - if you didn't put off the base raid for a while, there's a good chance you'll have missed the chance to stun a regular Sectoid or a Thin Man for interrogation, and they more or less stop showing up after raiding the base, which without the Council missions would make them Lost Forever.
Operation Gangplank, the final mission of Slingshot. You're on a Battleship, but unlike late-game Battleships, this one is mostly crewed by Sectoids and Thin Men, and they show up piecemeal. Sure, a Chryssalid, a Muton, and a Cyberdisc show up later on, but those are singular in every instance, and are nothing a good team with Carapace Armor and lasers can't handle, especially when compared with the Muton rush that was the previous Slingshot mission.
Broken Base: With a series like this, it was bound to happen. Most of the players can be split into 3 groups:
The fans who love the game and believe that it's a worthy successor to the X-COM name.
The moderates and newcomers who don't really care about the history of the franchise but think it's still a pretty good game.
Complacent Gaming Syndrome: Some possible class skills simply never get picked, due to perceived or actual uselessness. Rarely will you find players with more than two snipers not trained with Squadsight, Supports without the Sprinter ability, or an Assault without Close Combat Specialist. Fortunately, Firaxis rectified these issues in Enemy Within, although now the skills to pick are Grenadier, HEAT Ammo (which is absolutely essential for fighting Mechtoids and Sectopods) and Squadsight (again).
Some of the new enemy types specifically address the overpowered nature of some class builds. Seekers now actively target isolated soldiers, including Squadsight snipers who normally hide at the very back of the battlefield. EXALT also forces a break from typical tactics, thanks to the fact that large numbers of them will swarm you on maps, reinforcements arrive every turn or so (so you can't simply press forward slowly and trigger one group at a time like with regular aliens) and they use your own tactics against you.
Sectopods. Enough health to require almost your entire squad's damage output to put down, high enough Defense to ensure a good portion of your squad will miss anyway, multiple attacks per turn and a free Overwatch shot, the ability to unleash (after one turn) a devastating area attack which, if you're unlucky, you might not see coming. And as a mechanical unit, it is impervious to most psionic abilities. Fortunately, a Heavy with Bullet Swarm, HEAT Ammo, and a Heavy Plasma makes scrap metal out of them, as will a full crit build Assault with Alloy Cannon, which can kill them with a single Rapid Fire if they activate Run & Gun beforehand (for maximum critical chance).
Face them in Impossible, and even your Heavies will have a hard time taking them down. But it can go even worse... you can face up to four Sectopods in a Terror mission. Hope you have Snipers with In The Zone ready to at least clear the drones.
And then in Enemy Within, Sectopods gain a passive ability called "Reinforced Armor". It halves all incoming damage, which in effect gives it around 60 Hitpoints at least (due to rounding if the damage is an odd number before halving)! If you dreaded encountering one before, you'll be shitting your pants in terror now. What is even worse is that the Heavy's "HEAT Ammo" ability now only gives +50% damage instead of +100%, which combined with said damage reduction means that Heavies are no longer the Sectopod-cheesers they once were. Oh, not to mention that because they still have 30 HP, this means that Drones effectively have their ability to repair Sectopods doubled!
Chryssalids in the early game. Their very long movement range (complete with In a Single Bound, so you're not safe even on the rooftops) and powerful melee attack (which can zombify any human it kills, to boot - even if it doesn't kill on impact, it's poisonous) makes them insanely dangerous, and they're very hard to kill until you get plenty of laser weapons, especially since they're resistant to Critical Hits. In the "Alien Base Assault" stage, they are very likely to appear and close the distance before you even get a turn, and can kill any of your soldiers in two hits (at most). It doesn't help that they're essentially Big Creepy-Crawlies – almost literally Demonic Spiders, albeit with six limbs, not eight.
Thin Men in the early-game on the higher difficulty settings. Incredibly mobile, deadly-accurate, twice as tough as they are on normal difficulty, and able to casually leap to higher ground. Many players have reported getting a total squad wipe on their first encounter with the Thin Men on higher difficulties.
The Mechtoids in Enemy Within are nothing to be laughed at. They have a lot of hit points, are heavily armed, can attack twice in a turn if they don't move, just like Sectopods, you can't flank them and if a normal Sectoid mind merges with it, it gets a psychic shield that allows it to tank damage even better. Killing the Sectoid that is doing the mind merging only does a little bit of damage to the Mechtoid. One exploitable vulnerability since they have to be piloted by a Sectoid, they are still vulnerable to psychic powers, so if you are lucky and mind control one, the tables can change very quickly. Additionally, the Sectoid pilot's cowardly nature will come out if the Mechtoid is wounded and there are several enemies in sight; it will choose to retreat (possibly using both moves) instead of taking down as many as it can, as Cyberdisks or Sectopods would.
Disappointing Last Level: A major complaint that's been brought against the game is the sub-par nature of the final level. It tends to feel rushed, like it was cobbled together at the last minute by ideas they thought would be cool but came up with late in development, and ends rather abruptly. Enemy Within, which brings so much new content to the game, has the exact same ending – the new alien units don't even feature in it.
8.8: 8.2 from IGN, igniting a mass of muttering and furrowed brows from dedicated fans. Metacritic gives it a solid-ish 89/100, brought down by one 70% review. Even Yahtzee liked the game enough to include it on his top five for 2012.
Ensemble Darkhorse: Dr. Vahlen, due to her actions and thinking well reflecting that of many XCOM players. While she may get excited at the sight of new technologies, she does show empathy for the soldiers and fear for humanity.
She still does whatever it takes to get the info she needs out of captive aliens. They tend to "expire" quickly. From their perspective she must be some mythical demon and the reason why you DON'T want to get caught alive by those creepy humans with their stun prods.
Pretty much all of the Hero Units, though this is deliberate.
A sniper with Double Tap, Squad Sight, and a Plasma Sniper Rifle is going to pretty much slaughter the opposition, especially if they have the high ground. In The Zone is also pretty broken, but relies on your sniper being in position to flank everyone, or all enemies being out of cover.
A pretty great way to get the high ground is via the Archangel Armor (especially so with the Advanced Flight Foundry project). If you fly high enough with that you're simultaneously unlikely to be targeted while also being likely to be in a good position for squadshotting enemies and providing far-reaching overwatch. A properly equipped sniper can end up being a critical attack fiend and even possibly your squad leader due to racking up kills easily.
With a Heavy to clear the aliens' cover and lower their health, an ITZ Sniper can kill all opposition, and still have a turn to spare.
Mimetic Skin in Enemy Within. Soldiers with Mimetic Skin have auto-activating invisibility if they move into high cover from outside enemy sight range, and can remain invisible in that position until they move or attack. And it becomes available very early in the tech tree. This enables extremely aggressive and risk-free scouting, ensuring that you will never run into an enemy ambush, and it also allows you to rain fire using a Squadsight Sniper with complete impunity. The fact that it has infinite uses makes it arguably better than Ghost Armor, a very late-game active stealth suit that many considered to be a game breaker to begin with. It can't stack with the Stealth ability from Ghost Armor or Grenade, and the fact that you need full cover can limit its usefulness in some maps... except for Major-ranked and above snipers, thanks to their "Low Profile" ability, which makes low cover count as full, meaning any kind of cover at all can trigger Mimetic Skin.
As noted above, in vanilla Enemy Unknown, the Ghost Armor can be incredibly powerful, as four usages can often be sufficient for most of or the entirety of the map in all but the longest missions. By the time you're going to be fielding Ghost Armor, chances are explosives and destroying alien equipment is going to be less of a concern for you, which is great because ambushing enemies with grenades or rockets becomes significantly more viable. Instead of needing multiple units or multiple turns to take down a single enemy, a lone Heavy or grenade-toting other unit can potentially clear out three or more enemies with a single attack. Chances are you might already have other ability combinations that are pretty powerful, but few things compare to the low risk, high reward strategy of ghosting. In particular, Terror missions become significantly easier when you can save civilians via a de facto victory over clustered aliens.
Now that a Snapshot build is finally viable, combine these for a ludicrous one. A Colonel with Snapshot, Mimetic Skin, Low Profile, and In The Zone is a walking hurricane of headshots, as they can slip undetected through an enemy line to take cover in the perfect position, then shoot them all dead the next turn.
MEC Troopers. Even with their basic starting loadout these guys have a huge minigun that will rip apart most enemies, and their starting MEC gives more health than any of the armor worn by normal soldiers except for the Archangel and Titan Armor, and the only normal armor that gives higher defense is the Ghost Armor. Though the MEC Troopers can't use cover, its Kinetic Strike Module system will let it One-Hit Kill anything short of a Cyberdisk or Mechtoid (and if upgraded, only Berserkers, Mechtoids, Sectopods and Ethereals can survive a hit from it), and its Flamethrower is easily among the best AOEs in the game that causes all organic units to panic if it doesn't kill them. All this before getting any of the MEC upgrades or class abilities, which in the late game can make a single well-used MEC almost unstoppable.
With Training Roulette, you can potentially get incredibly powerful characters by mixing and matching certain combinations of skills. How about an Assault class with Sprinter and Low Profile to help them close the distance with a shotgun and then be in decent cover afterwards? Low Profile also pairs well with the Mimetic Skin gene mod as it allows essentially any cover to trigger the free ghost stealth. You could even pair it with Muscle Fiber Density to leap up buildings or Adaptive Bone Marrow to make sure that even if your Assault does get hit, they'll be able to heal it up over time and likely recover quickly after the mission anyways. Even with the restrictions that covert operatives can face, with the right set of equipment and abilities it'd be like EXALT was essentially infiltrated by superman.
Units firing may bug out and be shown shooting in a completely different direction... but the rounds will still go right into their target.
Suppressing melee enemies will have them stand still out of fear of provoking a reaction shot from the ability, and can take no other actions if not adjacent to attackable units because melee enemies can only attack in melee or move. Of course, them standing still for a turn to let the rest of your troops get in position to shoot them to ribbons is more likely to be hazardous to their health than one reaction shot while they run for cover. Fixed in Enemy Within.
Snipers with Squadsight, when put into Overwatch with a pistol, can take reaction shots at sniper distance, which is incredibly beyond the pistol's maximum range in gameplay.
Sometimes, when using their sidearm, your soldiers will still keep their primary weapon model on their hands, so this can result in your trooper holding a plasma sniper like a pistol and shooting regular bullets.
The Ethereals' attack reflector doesn't work on missed shots from an Assault's Rapid Fire skill, and if it reflects the first but gets hit by the second, the first shot won't be reflected.
If a Mind Controlled alien is killed, they're treated like a fallen squadmate when it comes to their gear. That is, their inventory is salvaged after the mission, so you often receive bonus Plasma weapons and grenades.
At least in Enemy Within, Floaters can now get themselves stuck on terrain, and waste both their moves trying to escape, leaving them sitting ducks for your soldiers.
Spontaneously, the weapon camos in Enemy Within can bug out and leave you with the default camo.
Occasionally while travelling to the far side of the Earth (e.g. XCOM Europe to Melbourne, Australia), the Skyranger will fly to the north pole and teleport to the south, or vice-versa.
It's possible to ignore the Iron Man restrictions if you're put in an undesirable situation. note So long as the aliens' turn doesn't end, the game doesn't autosave. This means that, so long as you quit out of the game before it becomes your turn again, nothing that happened between your turn starting and the aliens' turn almost ending is saved.
On PC you can also just alt-tab out of the game and make a backup copy of your ironman save. When things go haywire (or your save is corrupted or something along those lines), just overwrite the current save with the backup save and you'll be able to pick up from where that left off. Though it's assuredly cheating the intent of ironman, it can help you survive the Early Game Hell on higher difficulties long enough to get to a point where things feel fairer, and then you can opt to use ironman as intended or just continue to defeat the purpose of using ironman in the first place.
PC-only and related to controls: Using a mouse lets you more precisely aim a grenade or rocket, but using a console controller (e.g. Xbox 360) seems to let you extend your maximum range via analog sticks at the cost of being noticeably harder to aim. Depending on the positioning of enemies, this extended range could be enough to give you the edge on a turn when enemies are clustered but far away.
Floaters; unlike the original game, many players actually hate them now.
Thin Men as well, as they're highly mobile like Floaters, and pack the same amount of firepower. Sure they die in one shot (unless you shoot them with your basic sidearm or are playing on Impossible) most of the time, but they have the annoying poison attack (which reduces a soldier's Aim) that never misses and they explode into a cloud of poison when killed. They're especially good at flanking injured troops at just the right time to deliver a killing blow...
In Terror missions, you can constantly hear air raid sirens going off and people screaming during the mission. The death cries of killed civilians are also this, especially if they are killed by a Chryssalid.
Each alien type makes its own unique noise when you can't see them. Sometimes, your soldiers will hear the aliens (accompanied by a visible wave of sound from the direction it came from) if you haven't encountered any in a while.
Jake Solomon's "That's XCOM, baby!" whenever something goes horribly wrong or wonderfully right despite being very unlikely. Missing with three 95% shots in a row or succeeding with a 10% Mind Control attempt? That's XCOM, baby!
Vahlen's requests to preserve the aliens' equipment can get rather annoying on harder difficulty modes, where fighting without extreme prejudice (read: explosives) is generally out of the question. It's gotten to the point where Firaxis included the option to turn it off in the Enemy Within expansion.
The advisers' urging you to hurry things up during some Council missions can get pretty annoying.
If you find yourself in a situation where you can see a group of Chryssalids and they can't see you, you'll come to regret it fast. They start roaring every 6 seconds, and since they don't start at the same time, you'll hear a never-ending stream of screams until you finally move.
In escort missions, not only are the civilians you need to escort utterly helpless, they also tend to make a brief speech every single turn – irritatingly freezing the game interface until they're done talking.
In the early game, losing soldiers with an Arc Thrower during a UFO mission is horrible. Not because you lost a soldier, or because you won't get to interrogate anything, but because you'll have to hear Dr. Vahlen bitch about you killing the Outsider instead of capturing it.
Alien death cries, especially Chryssalids when they let out a loud painful shriek when you shoot the last life out of them. Each one you hear means you have successfully taken out something that was trying to kill your men and anything that looks like your men.
Your advisers' compliments when you complete a mission without any XCOM soldier even getting injured. Feel proud, you deserve to.
Even better than this is the Council telling you what a good job you did if you get an A grade at the end of the month.
The Run and Gun sound effect (optionally followed by "Moving at the speed of death" or "Gun 'em down"). Well, except for the times when your Assault charges in to give one hapless alien a faceful of shotgun only to aggro six nearby Mutons (unless you have explosives to blow them up with).
Any time you mind control something. The Mutons (any type) in particular make this deafening roar as you do. Given how much of a pain Mutons are, this makes seeing one do some of the work amazing.
Paranoia Fuel: Seekers. Once they show up in a mission, you've pretty much got to drop everything and put your entire squad into Overwatch, because they're out there, hunting you, and if you drop your guard for even a heartbeat, one of your soldiers is getting strangled.
The Scrappy: Central Officer Bradford is not popular with some fans, probably because the first thing he does in game (at least, if the tutorial is activated) is command the very first XCOM squad to their death leaving only one survivor, and from then on seems to make it a point to act in complete Genre Blindness. He's also a rather generic crew-cut military man, with little characterisation, making him hard to like even disregarding his bad decisions.
Rescued from the Scrappy Heap: The "Security Breach" trailer from Enemy Within has changed this, though, simply because Bradford is shown beating the crap out of a mind controlled base technician.
If you fail the mission where the aliens attack XCOM HQ, a cutscene plays showing Bradford's dead body propped up against the wall and with a pistol at his side. Lying in front of him is a dead Sectoid. The implications are profound.
The second special Council mission, "Confounding Light", from the SlingshotDLC. You have only ten turns to find and activate four beacons, all of which are heavily guarded by poisonous Thin Men, who start receiving hard hitting Muton reinforcements (who pack full-sized Plasma Rifles instead of the Light ones they normally have early on) after a while. Putting it off until your soldiers have some better equipment is advisable.
Enemy Within gives us "Site Recon", which tasks you with exploring an abandoned fishing village that has gone silent after an alleged alien attack. It turns out that the entire town was overrun by Chryssalids and is now infested by Chryssalid zombies. But wait, it gets better. The source of the infestation is a fishing ship with a whale carcass that the Chryssalids are using as a hive. Understandably, Central decides that this entire town can fuck right off and calls for an airstrike to purge the area. From there, you have eight turns to make it back to the opposite corner of the map for extraction while fleeing from an endless wave of Chryssalids spawning from the hive. Unless you can cleverly strategize and get a few lucky rolls, you'll probably lose people, either from the Chryssalids or from simply being left behind. Though if you get this mission late enough, it can turn into cakewalk instead, since no enemy unit can shoot you, Archangel armor can make you practically invincible here. Having a squadsight sniper with Archangel Armor means that they can easily kill any enemies that dare move into his/her line of fire. Power-armored assault troops and well-upgraded MEC troopers can also slaughter the Chryssalids by the dozen in the late game.
The player's first Terror mission, bonus points if it's their first play through too. It comes early enough in the game where you might not have a lot of upgrades, and is the first time you encounter Chryssalids. That's bad enough, but there's tons of civilians scattered across the map, who are being killed by said Chryssalids, if the player doesn't kill the Chyrssalids and any Zombies fast enough, they'll get swamped as the number of enemies multiply.
The level "Street Hurricane" is referred to as "Murder Street" by some players because good cover is sparse, its linear design means there are few flanking opportunities, and the size of the map means activating multiple groups of enemies at once is quite likely. At least until you get Squadsight snipers on the roof of the bus stop, in which case the long distance and poor cover can work in your favor.
The level "Demolition" was infamous for its design immensely favoring the defending aliens. With the few good covers lumping your squad together as grenade bait and often breaking line of sight, the approach giving the aliens the high ground, and the only flanking route long and tedious with zero cover if you're spotted, players winced whenever they saw the map on the briefing. The map holds the (dis)honor of being the only level so unbalanced that it was overhauled in Enemy Within.
They Changed It, Now It Sucks: The most militant of X-COM purists despise Enemy Unknown because Firaxis had the gall to modernize most of the game features and streamline some of the more archaic gameplay elements that plagued the original game.