Enjoyable, a little frustrating
I love the style, it looks the part, the only thing that annoys me is the inconsistant difficulty, I am stuck on merely 3 levels that stop me from progressing, and although I probably just suck it have enjoyed it immensly. The range of enimies, although small, is quite varied, and really inventive combinations of them creates a large set of excellent levels.
Co-op is something all games should have, it is an unbeaten experience to have a friend sitting next to you that you can scream at, and I love the co-op on N+, never fails to entertain.
Try the trial, then buy it