Wow you're surprised that people are still wanting to play Halo 2? Really?
On the PC and G4WL, yes - especially since the FPS arena is VERY crowded on here and there's a lot of great ones on the market, to say the very least.
EDIT:
Hmmmm...on 2nd thought, you can get Shadowrun and Halo 2 for the PC both VERY relatively cheap, these days and age. Plus, most people w/ Vista and Win 7 can probably easily run those two, as well. Yeah, that might help matters, come to think of it...
EDIT #2:
That would be more interesting if that wasn't pretty much every GFWL enabled title of note.
Hey, Kane & Lynch: Dead Men is missing from the list.