Arrow keys to move, Space to shoot.
Far from a complete game, but playable.

Each new enemy which spawns bases its stats on the average of the surviving enemies so in theory they 'evolve', in practice it makes very little noticeable difference, although they do tend to get faster. I'm sure the concept could be done well (in fact someone nearly certainly will have done something similar and better in the competition) but I don't have time to do it.