TF2
Funny, Fast and Free

L4D2
Fast paced and quite good graphics

Portal / Portal 2
Now you're thinking with portals

SpaceChem
You thought portal 1 and 2 were hard?

Borderlands 2
Use more gun

Half Life 2
Not the newest, but still good


Kerbal Space Program
Spaaaaaaaaaaaace (And explosions)

Frozen Synapse
Guns, logic, rockets and more logic

Just Cause 2
Why? Just (be)cause

Skyrim
Fire or ice, why not BOTH

DXHR
Who says games cannot challenge moral issues, and be great games at the same time also.