De85 on 11 October 2010
Shadow Complex for sure. If you're obsessive about finding all the upgrades you can spend upwards of 10 hours on your first playthrough.
Castle Crashers is unbeatable if you're into coop.
Splosion Man is great for platforming, and is more difficult than most XBLA games out there if you're looking for a challenge.
Geometry Wars 2 is also a good time sink...
As always try the demo first, but these are my top recommendations
