I experienced something weird the other.. month. Me and my cousin were playing Halo 2 split screen co-op and were having fun. The graphics in Halo 2 made it somewhat difficult to see where you were going on only half a screen, but it was ok. Then, a week later or so, my cousin came over to my house and we had nothing to do, so I tossed in Timesplitters 2 for no reason and to my surprise it also had a split screen co-op mode. Imagine our even bigger surprise when it turned out that the co-op in Timesplitters 2 (on my PS2, but it's out on Xbox too) was a lot MORE fun than the split screen co-op in Halo 2! Not only is the graphics clearer (and easier to see on half a screen), but the action also felt better, the weapons made more of an impact and even the levels felt superior in design and scope. Weird, since I've never really heard anything about Timesplitters 2 and Halo 2 is supposed (according to a lot of Xbox-players) to be God's gift to multiplayer.
Halo was a great premiere title that seemed to take advantage of the power of the Xbox right from the start. Halo 2 was just more of the same, but shorter and with a very unsatisfying end. All in all I think the Halo's are way overrated, as there are lots of better games on other systems, but I can imagine that for a Xbox-owner that played Halo as his first title, it must have been impressive.