Get it for the xbox, not the PC. The PC has online that gives you a weird, glitchy lag. At least if you play on XBC the lag is just bullet lag which can be compensated for.
Otherwise, the game is easily my favorite of the series. The story is nowhere near as convoluted as halo 2 or 3, and imo the levels are just more fun to blast through. I like the fact that you get little crests over the campaign levels when you beat them on different difficulties to let everyone playing on your xbox know if you have beaten everything on legendary or heroic or w/e.
As Yuke said this game plays very different than the other halos, but the differences are mostly improvements over the later games which cater largely to a more casual audience that did not like the frantic, fast paced, and more challenging gameplay elements of the first game.