I succumbed to the Halo hype and bought a copy on opening day. It's a fun game, particularly the cooperative multiplayer. Nothing like Bioshock in terms of artistic merit, but good AI and strong gameplay.
But there's one big problem in the game; it looks kinda crappy on HD screens. Huge jaggies everywhere. I've read different explanations as to why; either the max resolution is only 640p (I don't quite buy it; 720p is way more likely. Update: Bungie confirms they render at 1152x640) or else they've limited themselves to simple 2xAA instead of better anti-aliasing. (A friend tells me his beautiful Xbox 360 game does edge detection and smoothing. Cool!)
I guess it's a tradeoff; they have some impressive HDR lighting and very complex models and the framerates have to be solid. And of course once the bullets are flying you're not watching the jaggies. Still, it's a shame.