This is both really polished and quite a nice little chunk of gameplay. I feel as though it could maybe do with a Portal-style introduction to the agent-swapping mechanic (where you more or less see it happen before you get to do it at will), but only if you add more levels - as it was, working out how the A and B rooms interacted was most of the fun.
I'm not sure if it was because I was playing this in WINE, but it took a while to get the sliding block to do anything. (It needed a double-click, which wasn't anywhere near the first thing I would have guessed.) Whether or not I was running into technical difficulties, I really could have done with some indication that there were two types of cubes that behaved in two different ways
Overall the sliding puzzles felt like the strongest bit of this, though: seeing the one cube move around both rooms was pretty neat (and in hindsight might make for a good introduction to the game).