This game COULD be good, but it just is not fun. After a while of playing i got invincible (maybe its just me). i could not lose unless i tried. At least make the game get harder. adding more time to the next wave does not really make the difficulty change. the gun shoots so fast that i just click once and the enemy is dead. Also make different enemies instead of the same portal thing. There should be different levels with obstacles to make the game difficult.