Don't Look Back is a cool little poem of a game, by Terry Cavanagh. I am an unabashed Terry Cavanagh fanboy, and have been so since I first played VVVVVV. This latest game (latest for me-- Cavanagh produced it in 2009) is a great entry into his body of work. With just 4 colors, a great soundtrack and basic gameplay, Don't Look Back is a compact little sonnet. It could have been more, but it didn't have to be. About twenty minutes in total, I recommend it.
note: I originally played the game on my phone, but eventually switched to playing on my computer over at Kongregate. I just couldn't handle the touch-screen controls. I need to play my platformers on a proper d-pad.
I only played the first batch of levels, as I downloaded the free version for Android. I will probably buy the full version as they don't ask much for it. Also available to play online at armor games.