To add: Desktop Dungeon with Derek Yu's tile set. Short-form "roguelike" that is actually more of a puzzle game. Takes less than 10 minutes to play a complete game.

I am on mobile right now, but search TIGsource for full links.

And to add to the discussion: games that I play the most are either online, procedural, or score-based. But games that I have enjoyed the most have all been highly focused, incredibly polished single player experiences. 10 years ago, these were long (30+ hour) games. But the cost of producing content has risen so much lately that you can only obtain this level of polish if you keep it short.