This game took me completely by surprise. I recently picked it up in the Humble Eye Candy Weekly Bundle, in which it was included for its aesthetic. I hadn't read anything about it yet, so I decided to just fire it up and go in cold. What I ended up playing was one of the best games I've ever played that uses music to engage the player with the gameplay mechanics.
The game's pretty good about ramping up the difficulty moderately, introducing new stage mechanics at a decent pace. The only time I really felt it was at all unfair about it was the boss fight at the end of Level 2, which seems to just involve guesswork if you don't know the pattern already. The rest of the time, my deaths were due to my own mistakes, either getting off rhythm or trying to rush too soon. Getting a feel for the rhythm of the music is crucial to successfully navigating a level and completing the boss fights.
The visuals are minimalist, but colorful, with the backgrounds pulsing in time to the music as the stage elements change. The bright palette is in stark contrast to Limbo, which was directed by the developer of 140, and it fits well with the electronic soundtrack (which I'll likely be purchasing).
The game was fairly short, as I finished the main levels within a little over an hour. There are additional levels which are mirrored versions of the main ones, but they're without checkpoints. I'm not sure I'll ever be able to finish those, but they're an option for those looking for an even greater challenge.
I'd advise using a gamepad if you're more comfortable playing platformers with one, even though the controls are very simple (just directionals and jumping). As you can imagine, it's unfortunately not a game I'd recommend for anyone who has difficulty with hand/eye coordination.
I thoroughly enjoyed this game, especially at the price I bought it at, but even at its (low) full price, I'd still recommend it at its short length, just for the simplistic brilliance of the way it melded gameplay and music. Even though I probably won't be able to finish the challenge levels, I'll probably go back to play through the old ones just to re-experience them.
If it's playable for you and you're a fan of platformers or music games, definitely check it out.