A Game About Game Literacy
Damian Sommer created this short, no-frills little puzzle platformer, A Game About Game Literacy, to throw the player into a series of one-screen, "extremely distilled metroidvanias." He accomplishes this by first teaching the player some rudimentary game mechanics and then builds upon those rules incrementally while increasing the difficulty and complexity of each level's design. And it works quite nicely for a game made in just a day and a half.
Follow the hints provided in the title text and note the use of the symbols introduced in each level as you make your way to the happy little green and yellow critter that marks the exit. Use the [arrow] or [WASD] keys for control, [M] to mute. There is no save feature or level select screen, you'll have to play through the game in one sitting. Forgivable when you consider the extremely short development period.
It starts out pretty basic, but keep with it: It'll get interesting, don't worry.
Seizure Warning: Strobe effects used in a couple of levels.
Thanks to Blue and Redmug for suggesting this one!