I want a fix for occasional crashing, which just started the other day for some reason, though not frequently enough to really put me off it
The biggest fix of all is VOIP, though it seems like a third party will beat them to it if TeamSync with TeamSpeak really works the way it's supposed to.
There are also some oddities in the lag hiding algorithms. I'd like lag to be obvious (I don't see a way to determine my ping from in game, and the server browser only sometimes gives me an actual ping), not just a nebulous feeling that somehow I'm inexplicably sucking a lot more than usual at shooting and not being shot.