Sanctum 2

I could never get past the first few scenarios on my own, and I don't have any friends who I can co-op this with, so ... I get the overwhelming impression that co-op is necessary to progress, despite claims to the contrary by the developers. Am I really just that bad at this? Either way, Sanctum 2 doesn't make me feel good. :( It's such a neat concept--I wish I could have enjoyed it!