Aether by Edmund McMillen and Tyler Glaiel
This is an interesting and engrossing game created by Edmund McMillen and Tyler Glaiel. Charming visuals and an atmospheric, dynamic soundtrack help to keep you engaged in this surreal puzzle platformer.
If you want an explanation of the game you can watch the interview with artist Edmund McMillen in this excerpt from Indie Game the Movie.
Use the WASD keys to move and use the mouse to fire at clouds and propel yourself upwards.