i still play it somewhat often. i'm Mythic atm, and hoping to rank up another one or two before next christmas when halo 4 comes out. a few other old games are starting to cut into my playing time, but it's still a lot of fun.
and i would have to agree it's the fps which takes the most skill to be an all around good player.
I'm a Forerunner but it means squat. My k/d on my main account is a .95 but when you actually go for objectives it kinds hurts your k/d. I have a 2nd account that has a 5.5 k/d in which I simply kill camp and be a fluff, doing multi-team king of the hill and getting 100 kills in a single game is quite fun ;)