I adore how little graphics eventually matter. Of course at first good graphics can be such an enormous pleasure, so breathtaking, and can add a great deal to the experience of playing a game. But in the end, mechanics always wins out. Quick example: the recent Prince of Persia game. Utterly beautiful, but I couldn't care less after an hour of that tortuous tedium. Opposite example: The Walls Are Not Cheese. You control a square who fires squares at other squares. There's about eight colours in the whole game, and it's compelling fun.
Your purple square fires pink squares at the world. These are used to either destroy "monsters" (blue squares) to to erode the scenery, which we're assured is not cheese. As you destroy it, and indeed as enemy squares fire back, debris is created which you scoop up by holding Shift. This refills your fire power, which becomes essential for finishing levels.
The goal is to reach the larger blue square and destroy it, which brings you into the next level, until rather sadly the game seems to just sort of stop. However, before you get there you experience some really smart ideas. My favourite aspect of the game is the danger of vacuuming up the debris: when holding down Shift to pull it all toward you, you also draw in any enemy fire. So if a shot has disappeared off screen but not yet hit anything, it can suddenly come swooping back in demanding quick reflexes on your part. It also leads to some excellent forehead-slapping deaths as you forget and suck all the murderous bullets toward you in the stupidest way. Firing also causes propulsion, so jumping and shooting can often lead to other interesting mishaps.
It's a very smart idea, very well delivered. If only it were longer. It would remain satisfying to play for quite a while without needing to introduce any new gimmicks, but comes to a close all too quickly, probably as a result of its being developed for a competition, in this case Ludum Dare.
It plays in a browser, and is well worth your attention.