I made a post a long time ago after Modern Warfare 2 came out about putting doors into multiplayer that require you to open them or breach them. If anyone has played Rainbow Six Vegas you will know how much fun it is sometimes to make a trap by the door. They could also make the doors have the option to be locked. I'm not saying encourage campers (maybe) but you could have some new equipment options, spycam to see under the door, a door ram (one of those lol moments thinking of what could top riot shield) and maybe a lock pick to go in silent.
Now, if you didn't have the equipment to open a locked door all you would have to do is shoot out the lock. Think about the objective gametypes though. If you could close a few doors and make a good defense and the offensive players could still get in silently or by going load.
It could possibly encourage some to use more team work (ya right).
What do you guys think? Flame me, troll me... I don't care