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.
This game is like a mix between Super Meat Boy (insane difficulty) and Portal (cool new ideas (and incidentally also infinite falls through "circular levels")).
At least unlike Super Meat Boy, it is nice to non-hardcore players by giving the option to play at slower speeds, with invincibility or even unlock game modes directly, just so you can have some fun without being constantly frustrated and giving up on the game. There are also a lot of checkpoints, which helps a lot. Like in Super Meat Boy, you respawn almost instantly (at the last checkpoint), making dieing less frustrating.
If you like it insanely hard, just leave all the default settings on. And after that, there are still enough achievements to unlock, like playing through the whole game without saves and without dieing...
There is also an unlockable secret lab with a "gravitron" level, where the goal is to survive as long as possible.
Apart from being challenging and having interesting gameplay mechanics and level design, the game also has a lot of humor.
Each level section has a name, and those names, when not funny on their own or well describing the current level, make sense once you continue ("What lies beneath?", "Doing things the hard way"). :)
The dialogs and terminal logs are also quite fun. All the characters have different personalities, which even makes it fun to replay certain sections (the "intermissions"), where you have to guide another character through levels. Victoria for instance is always scared, while Vermilion is all excited about the horrible/weird things happening to them! :D
-The difficulty is a bit uneven. Some hard parts at the beginning, and easy parts towards the end.
-Exploring the relatively safe surroundings to locate the entry points to the various "buildings" or some of the trinkets can be a bit boring and tedious sometimes, as you have to cross great distances, falling up or down. There are a lot of "empty screens" on the world map.