- Broken Base: In V MGO, the Fulton Punch. The Fulton Punch is a technique that allows you to instantly KO an enemy player and extract them via Fulton Balloon instantly. Some players complain that it completely breaks the game's balance by introducing an overpowered way to score free Fulton Extractions, while others state that it's balanced because it takes skill to use, and whiffing it is basically instant death.
- Contested Sequel: While MGO as a whole has its fair share of quirks that make it stand out over other shooters, the third installment got some flak for "dumbing down" the gameplay. Less overall time-to-kill on any given enemy (including the supposedly durable Enforcer class), run-and-gun gameplay, and plenty of opportunities for Grenade Spam (complete with the Demolitions Lv2 perk dropping a grenade on death) have led to some people unfavorably comparing MGO3 to the Call of Duty series. Some have even gone so far as to quit MGO3 in favor of returning to MGO2 through the Save MGO fan project, even with the constant server problems plaguing it.
- In Snake Eater MGO, there are times when players may seem like they are randomly dying, though they are technically killed by an unseen and unheard player (their weapons are silent).
- As in the main game, the shotgun is ludicrously overpowered. Many servers banned it.
- Petrol Bombs in TPP MGO can be a notoriously unfair weapon. They can be thrown a fair distance, explode a wide radius and set everything nearby on fire. And fire damage can be a near instakill. Making matters worse, is if the connection is poor, players can spontaneously combust and die even if the flames aren't visibly near them. Not even water stops the flames from these little things. The only counter to getting burnt to a crisp is to quickly equip your cardboard box. If you don't have one, well...
- Walker Gears in V are obscenely powerful to the point where it isn't even funny. The frontal shield ensures that you can't shoot a Walker Gear from the front and expect to kill its driver, and the thing is as hard as a brick, preventing anything that isn't another Walker Gear, an emplacement, or basically an entire team armed with assault rifles from blowing it up. The mounted minigun rips apart anything in its sight, and despite it's large spread, getting in front of a Walker Gear without a Riot Shield is almost certain death. The only things that hold it back are the overheat mechanic preventing you from firing the minigun forever, and the fact that being near one before and after it explodes will most likely kill you. Version 1.01 severely nerfed it to the point where it's only primary use is a fast method of transportation.
- Infiltrators in MGO3 used to be this. Their exclusive non-lethal shotgun had an absurd knockdown range, making subsequent shots easier, and it was almost laughably easy to get random stuns by throwing stun grenades everywhere, not helped by the fact that an ammo count-increasing perk for support weapons accessible by all classes allowed infiltrators to carry five stun grenades. Those that instead specialized into Fulton extractions got to enjoy the benefits of having Fulton balloons that were way too durable for the very brief amount of time they stayed on-screen before taking off. Later patches eventually nerfed all of these aspects to the ground - the shotgun's knockdown range became so short that CQC was usually the better option, the one-hit KO radius of stun grenades was severely reduced (as well as limiting the carrying capacity to three at best), and high-level Fulton balloons got their durability decreased.
- All three unique characters in MGO3. Unique characters in the previous installment either had higher-but-not-broken amounts of perks (Old Snake, Meryl, Johnny, Liquid Ocelot) or a completely different playstyle (Mei-Ling, Raiden, Vamp). Venom Snake, Revolver Ocelot, and Quiet manage to somehow be both of these at once, and then some.
- Before even getting into each character's unique abilities, it should be noted that all three of them have some combination of perks that would require dozens of perk slots to accommodate. Normal players only get four of these slots.
- Venom Snake brings his prosthetic arm over from the main game. It's perfectly possible for the player controlling him to simply camp at their own spawn point and Rocket Punch people to death from afar.
- Revolver Ocelot somehow manages to make is Improbable Aiming Skills even more improbable by making his bullets home in on marked targets after reflecting off a wall (as opposed to semi-realistically).
- Quiet's sniping skills give her quite literally zero recoil on all sniper rifles, her Flash Step briefly renders her invulnerable (the only other thing in the game that grants invulnerability is teleporting with the ER-B Wormhole Generator), and her melee attacks are quicker than the average soldier's, only outmatched in stun damage by the CQC of Snake and infiltrators specializing in it.
- Most Wonderful Sound: The "kashing!" when you nail a headshot. Of course, it may not be this for the opposition, since when someone lands a headshot, everyone hears it.
- Older Than They Think: MGO2's Stealth Deathmatch was a last man standing mode which includes a circle that closes in and drains the health of players outside of it almost a decade before Player Unknowns Battlegrounds and Fortnite achieved mainstream success with that formula.
- Scrappy Mechanic:
- The cover system in GOP MGO. While Snake Eater MGO's leaning against the wall and popping out to shoot was fast enough (provided the enemy doesn't provide a quick headshot), the actual cover system is not as helpful, or even as intuitive as, say... Gears of War or Uncharted. Popping out to shoot isn't as instantaneous as you'd hope in a fast paced shooter, and sometimes you will feel like you're glued to cover. Don't be surprised when you see many players taking cover without actually utilizing the cover mechanics.
- Perhaps the system that GOP MGO was built on to begin with. For beginners, you had to be extremely lucky to access the beta since servers were incredibly hogged up, and the online service you have to register for would constantly crash during this period. On top of that, you need not one, but two user names. One of them logs you in to the website, and another logs you into the game. On top of that, it isn't even stable. That probably contributed to GOP Metal Gear Online's relatively short life span.
- Arguably, the original Sneaking Mission. It's not so much that stealth is a must, but the game mode can be beaten by having Snake dash at one of the two microfilms, and dashing back to one of two of the check points. Snake Wins! It's also just as easy to take Snake out, so many players do not see the point in attempting stealth.
- The Sneaking Mission in the GOP version of MGO does attempt to encourage stealth, but now it's incredibly difficult for Snake to score. Not to mention a kill means he loses ALL the dogtags! A patch did ease the pain a bit by making Snake lose only one dogtag at a time, instead of all two.
- "Stop Having Fun" Guys:
- At least for Snake Eater MGO, many players would scorn over anyone who dares to bring a shotgun into the game, prompting the host to start kicking players using that gun.
- For Portable Ops, is the server you are trying to access actively restricting you from entering because you have a weapon the host doesn't like? Too bad! You have to go all the way back to the game menu to change your equipment, and spend another few minutes reconnecting and joining again, provided the same server even shows up...
- GOP MGO players really hates the M14, because of how it acts as both a semi-automatic sniper rifle, AND as a fully-automatic assault rifle. Konami did attempt to balance it out by making it one of the more expensive weapons to purchase.
YMMV / Metal Gear Online