Too long
To sum it up, its too long. I played this for ages, it never really got any harder. I gave up around wave 27 or so out of sheer boredom. I never even really came close to dying. Does it have an end?
The music, weapons and 'feel' of the game is all very steampunk.
I found some serious inbalance in the turrets, the most expensive turret is useless, it fires so slowly that it rarely hits and only 1 shots the weakest of enemies, the cheapest turret is vastly superior to it.
So it needs to end sooner (or just end if it does not) and the difficulty curve needs to ramp up way faster.