Nice game; it employs a good mix of requiring both luck and skill and beating it was certainly one of the most difficult things I've done today (the final boss didn't die, but I survived with 5 HP anyway), as it's also mercilessly difficult. I'm really digging the random, semiroguelite-ish aspects of the game; making you choose how's the wave gonna be and not knowing which tower you'll be getting add to the overall experience and pushes your game as a fresh & new thing in an otherwise overdone formula of TD. The graphics & sounds are nice, too ;)
Edit: after the update, I can no longer say that it's mercilessly difficult (yeah, I kinda came in here just to brag that I went through the whole thing again, but now without losing a single hit point >:]). Still fun, though.