Could have been better. Could have been much, much worse. I rented The Marsh because I enjoy a good Gabrielle Anwar film. Actually, those are few and far between -- the truth is I'll watch anything she's in. I must say this is better than most of the movies she's done (likely thanks to the absence of Craig Sheffer).
Her character was well defined and complex, but she seemed more curious than frightened. It made sense when she spoke about how fairy tales are supposed to give kids the willies, and that's what kids like - I had a copy of Der Struwwelpeter when I was a kid - but this film wasn't really scary or anything much more than creepy.
I had braced myself for the worst, and was waiting for one of the two clichéd scenes, you know the wizened old man who says "you don't know what you're dealing with here'" or the abrasive and skeptical sheriff / authority figure who knows more than he lets on. So it was refreshing when Whittaker's character moved the plot along as quickly as it did.
The opening scene was marvelous, and the scene with her therapist could have been great with some smoother editing, but the flashlight in the dark videography is worthless. The death scenes are waaay cheesy. In the end, I'd say the director pulled it off, but it was touch and go there for a while.
All in all, this was a (bad) B movie, but with just enough sunk into the production to make it halfway decent.