I'd say a B is fair. The acting is mostly good. The visuals are great. Action sequences are actiony.
The plot left more unresolved questions than I generally like. The scientific method used by the supposed scientists was laughable. The biologist in particular was an idiot. Hissing snake-like thing with bared fangs = stay the fuck away from it. The average high school drop out should know that, but this supposed biologist doesn't?
Anyway, would probably watch again if it was on TV and I had nothing better to do. Maybe not though. Might watch the sequel once it moves to the cheap theatre.