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.
Complacent Gaming Syndrome: Many people got through Bad Company 2's entire campaign only with the XM8/AN-94 loadout, occasionally switching one of them for an RPG or a sniper rifle.
Multiplayer's not much better. Everyone uses the AN-94, M60, and GOL, all with Magnum ammo so they're capable of a One-Hit Kill at pretty much any range. The XM8 + Under-barrel Shotgun is also a very powerful and easy combination to use. Blam the first person you see with the shotgun and instantly switch to the XM8 to spray and pray anyone else.
Crowning Moment of Funny: Happens several times in Bad Company 1 (listen in on the first mission, when Haggard talks about Miss July and his cousin). Despite how serious Bad Company 2's campaign tries to be, it still has its comedic moments.
Haggard:"Shit, that tore it. Get outta my way, I gotta save me some cheerleaders!"
The game has a strangely-funny clanging sound that plays to indicate you've scored a headshot. Doubly funny is that, with some weapons, said headshots are not instantly fatal, meaning you can hear the sound repeatedly if enough bullets connect with the head.
The Bad Company 1 beta had a glitch where you could crush an allies light tank (the MEC one) by backing up into them in a main battle tank. Instead of just colliding and pushing the smaller tank, your MBT would literally drive up it and completely crush it- even causing the wreckage to disappear.
Game Breaker: The M60 in Bad Company 2. Even with its low rate of fire, its damage output at all ranges is still unrivaled by any other gun in the game. So overpowered that it and the 1911 got nerfed on the first major update.
The Apache gunship, especially when the pilot zooms around in circles spitting out rockets, getting tons of kills without even having to aim.
Good Bad Bugs: There was a bug which made almost all sound effects not play for a few moments in-game, especially when too many explosions or the like occurred at once near the player character. This gave an impression of the player character undergoing Shell-Shock Silence.
Harsher in Hindsight: DICE's constant mockery of the Modern Warfare series for ditching dedicated servers turned rather hypocritical after the launch of Bad Company 2, when the servers DICE provided for the consoles couldn't handle the traffic load.
DICE also mocked MW2's lack of mod support and hyped up Battlefield's promised mod support a great deal. Turns out, DICE wont add mod support to their franchise either. It was explained in an interview that this was due to limitations of the Frostbite engine, which was still a better explanation than "We want you to play the game the way we made it".
Nightmare Fuel: The Book Ends for Bad Company 2 that show Russia's territory expanding are extremely unnerving. This probably isn't helped by the fact that their territory looks a lot like blood, seeping over the globe.
Player Punch: Flynn is shot down for the second (and final) time, just minutes after your squad rescues him and seconds after his Gunship Rescue moment.
Almost all weapons (with the exception of grenades) usually wont work at point blank range if you're taking damage when you use them. Anti-tank missiles dont work at all if the player who fired them is killed before the missiles hit anything.
The tracer can lock on to any kind of vehicle, including the Apache. However, the Apache can fire a massive stream of rockets that will push back into hiding any recon class it doesnt kill outright. The Scrappy Mechanic comes in from the fact that even if you manage to successfully tag the Apache, it can drop countermeasure flares that nullify the effect of the tracer before anyone can even lock on. The only way to destroy it from the ground would be to fire at it yourself, which is about as easy as hitting a jet with a slingshot. For a while it was completely possible to win the match on your own by flying around the enemies' spawn spamming rockets.
In the Vietnam expansion, machine guns fired from the boats can inflict more damage than similar weapons used in the vanilla game.
They Changed It, Now It Sucks: Since the game was programmed with console audiences in mind, there's a lot of changes the Battlefield 2 PC community found annoying:
In multiplayer, all characters now have bigger hitboxes than in the previous games, to make it easier for game-pad users to connect their shots (compared with Battlefield 2, which had smaller hitboxes). Unfortunately, this had the side effect of mouse using PC players being able to kill at incredible distances, sometimes around corners, and caused the infamous "sticky bullet" glitch.
Gunships, which were massive Game Breakers in BF 2, were nerfed and had their TV missiles removed, armor weakened, and can now take damage from any kind of weapon.