I may check it out as a renter. I don't think you can expect great acting performances from unknown actors, you can only hope that you get them, so that isn't really a deal-breaker for me. (See: Evil Dead. (NO! I'm not saying that it was a bad movie; not at all! But if you think Campbell did an Oscar turn in it, then you are batshit-fucking-LOCO.)) I'm willing to endure a lot of bad acting for a good story, or even for good atmosphere-- Monsters might still provide the latter.
Personally, when I read that the director spent over a year doing the CGI himself, I kind of worried that maybe- just maybe- other aspects of the movie could suffer... and from Bob's description, I was entirely correct.