I'm playing Halo and enjoying it immensly.
I'm running 1024x768 - 4 xaa - 8xaf outdoors
and 640 x 480 4xaa - 8xaf indoors on my 9700.
all other settings maxed.
There are a few levels indoors that really lag bad without the drop to 640x480 but with 4xaa on the jaggies are gone
I like the levels in that there is lots of good terrain to fight on, not the usual endless flat corridoors of other FPS's. The reactions of some of the aliens are downright humorous as well.