Not to bad
It's a good idea and a good game, the graphics look great, the gameplay is smooth and I can find no glitches, it is a game which always keeps me moving.
But then that is half the problem, I find that with these sort of "swarm" games it is best to try and make counter-methods to stop a player camping one spot. Yours seemed to be the spiders. However this made the gameplay very unenjoyable and frustrating after a while. The spiders spawn directly in your position and at a constant rate making it impossible to stand still for even a second. Add this to the ridiculous number of enemies coming already and it essentially makes the game "shoot and run for 2 mintues!"
If you took down their spawn time a little (on everything) and stopped the spiders spawning on top of your head it could curve some frustration. Upon testing in the defence games it is MUCH easier there to hold a position however you still have the spiders constantly upon you.
Still a pleasing game but I don't think I would go for a second play with it unlike similar shooter games.