i've downloaded about half to 2/3 of the full game demos on XBL. Faves so far were Forza 2, Top Spin 2, Dirt (kind of), NBA Live 07, and a handful of others.
On Arcade, I've downloaded almost all of the games and tried them. I've bought:
Assault Heroes. Try it -- it's awesome. Kind of like a modern day Ikari Warriors... It has great graphics, bosses are fun, and has a 2 player co-op same screen. The difficulty level can be set to "easy" for co-op with the casual gamer in the household...
Outpost Kaloki. Kind of a sim-city lite.
Band of Bugs. Hard to say what to compare to. Sort of an RTS lite.
Boom Boom Rocket. Mindless sound and graphics.








