VVVVVV is a retro styled 2D platformer by Terry Cavanagh, creator of dozens of free games. You play as the fearless leader of a team of dimension exploring scientists who inadvertently crash, and are separated. The game involves exploring the strange world you've found yourself in, and reuniting your friends. VVVVVV explores one simple game mechanic: you cannot jump - instead, you reverse your own gravity at the press of a button. The game focuses on playing with this mechanic in a variety of interesting ways. The game is designed not to artificially gate your progress. In VVVVVV there are no locks, no power-ups, no switches, nothing to stop you progressing except the challenges themselves.
So nostalgic... it is a game were you die many, many, many, many, many times (I finished the game with around 1100 deaths), but it doesn't ruin the experience.
The soundtrack is fantastic.
It is a short game, but that worth every penny. Also, it has a lot of challenges too, aside from the "story mode", so it has a very good replay value.