Pretty Good.
I enjoyed it at first.
But it is too simple, and got boring fast.
On top of that, I played going on 20 minutes. There should be a time after which you win.
But really, too easy once you start. I had a giant wall of debris, 3 guys with fully leveled damage, and it wasn't too hard to keep it up after that.
Good though. I do like it. Throw in some improvements and it would be pretty damn amazing.