Played the demo of Bad Company though and deleted it after one game. It wasn't half as much fun or as polished/balanced as COD4's online if you ask me. I just couldn't get into it at all.
I become bored of FPS games pretty quickly if I can't change class. When classes are involved, I find there is more strategy, more options for fun play, etc. Also, I've learned over the years never to judge how polished or balanced a game is based on the demo.