I'm going to say it, I don't care how many people flame me. I hated Bad Company 2's multiplayer. Sure it's fun at first, but when I started noticing some things happening over and over again, e.g. getting spawntrapped with two helicopters, teammates not going for the objectives, everyone is a sniper, it pissed me off that this shit happened every single damn game and after a while I just couldn't have fun with it. That being said, the occasional tank kill with the AT mines is VERY satisfying.
Anyway, back on topic...dammit, I can't think of any that I enjoyed for a long time. It's a stretch, but CoD 4. Quickscoping aside, it was nicely balanced and there were no dumb perks that overpowered everything in that slot. Maps were nice and gameplay was fun.
PS. Before you counter my BC2 rant by calling me a CoD fanboy, I'll say this. It was my FIRST FPS game that I played online. I played CoD 4 and Black Ops later. So hah!