Thank you for your comment! Once you destroy enough spawners, you can slowly decrese the number of enemies. Also, at the end of each level you can upgrade your attack speed. When you die, you keep upgrades. I managed to finish all 3 levels without dying, so it is possible; but I know how the levels look like. You should be able to finish the game at the 2nd or 3rd try, but then again, there is no special winning screen (: