Splinter Cell and Ghost Recon are better on the GC (testimony from FAQ writers at GameFAQs who played all versions), so your point there has become somewhat mute.
Halo may seem nice to you, but it's puke bad to me. I guess it's genre doesn't help it much for me. I have played it, so you can't accuse me of "not knowing what I'm talking about" or anything.
Oh, and I think Takt of the Wind (GC Zelda) out-sold (or came very close to) Ocarina of Time. Master Quest was awesome, and it was actually #1 on the top selling games list until Takt of the Wind came out. I don't think Halo 2 will outstrip Zelda OoT either, but I do somewhat doubt it will outstrip a few other games as well.
In any case, isn't Halo coming to the PC and Halo 2 already scheduled for porting? So...what's the point now? You may as well stick with PC and get your kicks there for XBox. Now, XBox did look like a nice system to me at first (when it was first released), but started to look less so as more and more of its games started porting. I've seen far too many XBox games port to PC, GC, and PS2 to leave it as too great a system. Personally, I don't like any of their XLIVE (is that the name?) games right now. Why? They only have FPS and Sports online, and I don't like those genre.
Now...games that were ported from PS2 to XBox were better on the XBox, but they seemed to have even further options on the GC... Now, I really haven't played (or cared to play) any of the massive ports, many of them aren't that great. What I would like to play that is multi-plat are games like LotR: RotK (newest one). I'd also like to try an older game, Baldur's Gate. Vexx also looks somewhat good of a platform multi-plat.
Now, if you can name some XBox games that I like, I won't be too surprised. I think I have pretty blatently put out my point-of-view. If I haven't said so, XBox will be the third system I get...if I ever get to the point I can... But, I can never seem to recall the games I want that are XBox only...