Stale feeling
It was such an incredible game, with it's interesting gameplay and unique defence mechanism. The enemies were visually interesting and new ones were constantly introduced. It was so much fun... and then the last boss hits you. All goes well until his health is low. Then he just spams those time bombs that turn into missiles and there's no way to beat him, as he becomes too small to hit and too fast to follow with your mouse. It was such a jump in difficulty that it just left me with a sick feeling of disappointment that my fun had been spoilt so utterly. And then you have to start all the way at the beginning again. It was just such a letdown. The game would have been perfect if not for those dumb time bombs.
Otherwise, this is a unique and interesting game that you should definitely try. But good luck beating it.