It's a great game, I really enjoyed it. It really makes you feel badass when you kill a boss. And the upgrading system between levels is good.
The bad: You don't just continue from where you get killed. You have to start the level all over again. But, the levels are so short that I didn't really mind this.
The other thing is that you need a lot of space. It's easy to lose complete track of where you are. And because of the way you move in game, by the time you see the guardian flash it's probably too late. If you don't have much space, I wouldn't bother.