This is pretty cool as a prototype, nice job! I'd say it needs some progression (one-on one to one-on-multiple, think 1xL against 2xS, etc.), as well as some more map variation (channels, islands, hazards like a giant whirlpool, kraken, the works). As a final shape, multiplayer would be pretty cool, but of course that's quite a bit more difficult... But I for one would be there for it :)