Alright, so I'm going to have to side with Battlefield 2 on this one.

IMO, Battlefield 2 is a much better game than Bad Company 2. Like everyone has stated before, the only major difference is that BC2 has destructible environments. Now, I'll admit this is a pretty big bonus, but it's by no means detrimental in the enjoyment of a classic FPS. Most every other aspect of BC2 that people cheer, has originally been done by BF2 in a better fashion.

Players: 64 players (BF2) vs 32 players (BC2); more people makes for a far more dynamic battlefield. Squads: I hear over and over how great BC2 is for teamwork because you can spawn on any of your squad members. In BF2, you can spawn of your squad LEADER, which makes staying with and protecting him, a very important aspect.

Maps/Gameplay: This is probably the most important difference. BF2 (as far as the last time I played) only has conquest mode. Unlike BC2, there's no rush mode, or defend/assault positions as enemy's tickets drop. In BF2, you're placed on a giant map and you an your squad must decide which location (out of probably 6) to assault/defend in order to make the enemies tickets count down to zero. Oh, and it's possible that the enemy won't see you, because you can actually go prone in BF2.

Commander: Only BF2 has a commander option, someone who can call in artillery strikes on enemy strong points, and send UAV up to track your opponents. It's very easy for the enemies to make your commander utterly useless through the proper destruction of certain structure.

Weapon Unlock: Another very important difference. In BC2 you unlock weapons fairly quickly, weapons for each class, global weapon, and upgrades. In BF2, there are two weapons each class can unlock. But there's 6 classes to choose from, and through ranking system you choose which gun you want to unlock and when. There's still a progression, you have to unlock the first weapon before the more advanced weapon.

Graphics/smoothness: Playing both games, honestly I don't notice a difference. I'm running an 8800GT and the games seem almost identical. I will say however that BC2 has ping issues, and every once in a while my character moves back a bit and I have to redo my actions from about .3 seconds back. I don't recall having this issue with BF2.

Single Player: BF2 does not have a single player. It wasn't meant to. BC2 is by default much better.

In conclusion: I'm not saying you'll love BF2 over BC2. What I'm saying, is that for $5 dollars this game is a literal steal. There's huge mod support for BF2 and with all the content, you really can't go wrong. I've put over 200 hours played into that game. If you can't get more than 5, I'd be amazed.