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.
I don't usually give a full 10 to a game but I truly believe that this game was the best game it could be. The simple mechanic of flipping gravity makes exploration interesting, and unlike any other platformer you've played. The retro music is memorable and the difficulty can get insane. If you're a veteran platformer fan then don't miss out on this one.
Veni, vidi vici...