Atom Zombie Smasher A fun Risk style back and forth between humans and zeds. I recommend playing a modded version(easy because you can create your own) before diving in on vanilla. Mod it to be weighted to your side to get the hang of it.
Terraria - More of a temporay addiction, but fun. 2D minecraft.
Magicka - Funny and fun. Co-Op compatible. Awesome combination of elements to make spells.
Xenowar - For the Android platform, it is a low graphic XCOM: UFO Defense Clone. Plays quite well. Just as burtal as what inspired it. I got overconfident and wound up losing my entire team in one outing.
Fallout: New Vegas - Post-apocalyptic survival FPS RPG. Amazing. Despite the crash to desktop bugs.