Halo was awesome, and I expect Halo 2 will also be, but they're not as great as everyone tries to make em. I've played a total of six-seven hours of it and had gotten bored of it by then (though I'd still play it with friends and stuff; I've played multiplayer, co-op, and single player for Halo, but it just sort of got dull). I've played eighteen+ hours of Zelda, beat the final boss four times (maybe five), and I'm still itching for more.
As for the big title, I say Mario Kart. And another game that's coming out is Kirby's Air Ride, which hasn't gotten much hype, but it looks cool and it's made by Hal Laboratories, same people that made both Smash Brothers and the N64 Kirby game (very fun game, in my opinion).