So I might be a bit late to this party, but Osmos is ridiculously awesome.
In one sentence: Katamari Damacy meets Newton’s Laws of Motion.
You’re a blob, floating in space. You want to eat other blobs to get bigger, before bigger blobs eat you. There’s only one problem: you can only move by flinging bits of yourself away in the opposite direction, decreasing your size in the process.
I started playing Osmos and thought it’d be a simple diversion, which on one level it is. But then I got to a level where there were three Sun-like gravity-inducing blobs with regular blobs orbiting them, all orbiting around a central gravity-blob. I poked and prodded at this level for a good ten minutes before realizing I was essentially trying to compute low-energy orbital transfers in my head, at which point my head exploded. Anything that can make me start doing that without realizing it is pretty awesome.
Anyway, I highly recommend Osmos. Give it a whirl, it’s only three bucks.