New to the 360/Great games

Halo 3 is only a must have because of the massive online community, despite it's age. I think the only reason it's so large is Halo is such a generic FPS. Gears is awesome, but it can get repetitive. Other games you should play are...

Fallout 3, Oblivion, Call of Duty 4, Call of Duty World at War, Left 4 Dead and Bioshock.

All of them excellent games and in my opinion, with the exception of Left 4 Dead, all are Game of the Year materail, in which one of them is, unless Oblivion is too.

New to the 360 forum/stick thread concept.

Burnout Paradise

Mass Effect is a definite must-buy. The Darkness and Condemned ahould be played, even if you just rent them and beat 'em when you have spare time. I didn't find Gears to be anything special though, so you'd be better off with something like Halo 3 or COD4.