Portal is great.  I am a confessed puzzle game lover, and portal is a great puzzle game.  One might even call it a demo, rather than a game, given the brevity, but the mechanics exposed in that time are beautiful.

The tools is a reimagining of a required designer tool: The ability to create and destroy walls.  Or the ability to create doors that travel from any 2 places.  After that it's just AI, levels and a bit of cheeck.