I'll echo Battlefield: Bad Company 2 sentiments. It's supremely satisfying to drop a bullet straight onto someone's noggin, especially if that someone's another sniper with me in his crosshairs. And I like being on the far end of a map and still being able to interact with and support my teammates, dropping players they're having problems with, players chasing them, players they haven't seen yet but are lying in wait; very happy to be a team player. What's also supremely satisfying is spinning around to see an enemy racing up from behind to knife me and dropping him with a no-scope shot.
And even though I'll take flak for this (more than likely), I love sniping in Modern Warfare 2. The Intervention is my rifle of choice, and I'm trying to build skill with the ACOG. I've never really been given grief for sniping, probably because I hard-scope almost all the time. I do like quick-acquisition moments, which are many. The range and accuracy of assault rifles and even some SMGs is considerable with the more skilled players, so being able to snap off a torso or even headshot is gratifying.
In both games, I try to communicate as much as possible based on what I see. Not necessarily looking for praise or glory, but I like knowing I can provide a decent amount of support for my teammates (provided they're not being jerks).