Far Cry 3 or Assassin's Creed 3. Both are AWESOME. Far Cry 3 is generally more strategic/non-linear combat. AC3 has a more in-depth story and is more complicated.
FTL:Faster Than Light
Hotline Miami
If you wait, you could buy The War Z when it gets on Steam
Sid Meier's Civilization: V
Chivalry:Medieval Warfare
Tropico 4 (modern tiemz expandz or u r newbz)