Have to agree with hadokenstyle
It's a great game- and I'm not normally a fan of upgrade games where I cannot upgrade everything as it screws with my OCD- but the final wave is just WAY too difficult. That last achievement is pretty much impossible to get.
The game also seems to have some lag issues and it's not only screwing with my movement, but also my aiming. It becomes difficult to move at times- far more difficult than it usually is without upgrading speed, mind you- and moving my mouse seems to do absolutely nothing. Please investigate and fix these things if you can. Thank you.