I got it on Steam, but I know it's also available via the iOS App Store. It's a simple game and I bet it's nice on a tablet device. Yet I think it's lacking on the PC.
After a couple of maps it becomes a bore. It's the same thing, over and over. Perhaps I'm just dumb, but I can't even tell what's going on sometimes. The graphical style of the game is neat, but how do I recognize different enemies? Speaking of design, why can't I see all the health bars?
If you like the simplicity, then it's a great game, though.
I'd rate it 3/5. It's a cheap and simple game which could easily last some 2-3 hours. Plenty of gameplay material if you enjoy it.