one thing I've noticed with Halo is that a lot of people hate it when they first play, it takes a little getting used to, and the jeep control can be confusing. But play it for a few hours, at least until you get the first jeep, and have some fun with it - the jeep control makes perfects sense once you realise exactly how it works, the game has to sorta draw you in before you get totally into it.
IMO, the X-Box will always be better for co-op games because people want to play on big TV's and have there mates round - I don't think the PC version of Halo will capture the essense at all, it'll play just like any other FPS because you don't feel like you have backup. For example, when myself and my buddy play it, we have each others back, we watch for ambushes, back each other up, are sensible with powerups and weapons, it's a bonafide co-op enhanced game. Most people would agree that co-op mode is a lot more fun than single player. That's why I think the PC version has lost some of it's gleam, co-op is a major part of Halo's charm.
I mean, how many other FPS games have followed suit? - There's even a 4 player co-op FPS, can't remember it's name, but Wolfenstein on the X-Box and R6:Rogue Spear both have co-op modes. This may sound daft, but if a game has a co-op mode I'll usually buy it without even reading a review, because I know I can play it alot more freely, the way I like, sometimes it's fun to wreck the place in Halo, or tease the zombies into traps in Wolfenstein, co-op modes make this sorta tomfoolery more fun.
My bet is that Halo2 will be the best X-Box game ever, just like it's daddy.
Van-B