Tetris got its post; time to cover my other favourite video game.
N++ is, in my opinion, the best platforming game ever made.
Launched under the Metanet Software umbrella, the third in a series of excellent games by Canadian duo Mare Sheppard and Raigan Burns, it features instant restarts upon failure, great physics, simple and elegant visuals, an addictive soundtrack, no scrolling, and pure determinism.
Once introduced to all the elements that can appear in a level, you can understand each new level through visual inspection before it starts. No surprises. Easy to learn but hard to master. Everybody will find their skills challenged here.
The level editor with online sharing complements thousands of levels of increasing difficulty, separated between solo, co-op and race categories, and only cleared by series of 5.
If you play one platformer in your life, make it N++.