Here is a list of other BrainGames that I like:

Mild
          SlapShot DropKick Teeko Pentago Hex TacTix Nim

Medium
          Quorridor Quarto AvalamBitaka LinesOfAction 
Spicy
          Tzaar Zertz Dvonn Yinsh Focus
Why do I like these?
          abstract strategy (no dice, spinners, cards, etc.)
          quick to learn (up and running in no time)
          complex enough to play again (and again, and again...)