I think the main attraction of Halo 2 is what you're not particularly interested in. i.e. multiplayer and in particular XBox Live. I know a number of Halo fans who have said the main thing missing from Halo is XBox Live support. It does have LAN multiplayer but that means everyone dragging TVs and XBoxes around to someone's house.

I don't like FPS games unless they are multiplayer. Playing against AI just doesn't cut it for me.

BTW: I don't have an XBox that I play games on.