Have you ever played an unusual game? By that I mean a game that sets itself apart from the others by being different in some distinct way. It may be the setting, or unique game mechanics that just set it apart.

For example: Two games that made me think of this thread are
Gathering Sky


Submerged


In terms of games I have played:

Papo & Yo was certainly different in terms of it's subject matter but also in terms of the child-like creativity of the game environment

Hammerfight had a unique game mechanic in that you used your mouse to move around your airship to get a blade or hammer spinning below you to attack enemies.