1) Fix jumping to be more consistent and get you over reasonable obstacles/up small incline. Even if it isn't a final solution, as long as it knocks any movement issues way down the list of things that are frustrating people in combat.

2) Better (sound/visual?) indication of when you're being damaged or fired at. Feeling like you have no chance to react and POOF becoming a chicken before you realized you were being shot is going to frustrate people, especially those newer to competitive FPS play.