First off, let me say that I'm not a Shyamalan hater and I don't think this movie is half as bad as some people seem to think it is. That said, it's pretty flawed. There will be some spoilers in this review, so be warned.
This movie is definitely more about the plot than the characters. We just don't get to know these people well enough for them to be truly interesting. An exception is the head village elder, but he isn't a central focus of the movie. The other exception is Adrien Brody's character, but that's because there really isn't much to know. He's mentally challenged and has a fixation on Ivy that turns violent. That's all there is to him. Lucius is quiet and brooding, but we never learn why. Ivy is blind, nice, and kind of a generic love interest. Those are our two main characters. The actors do a great job and make them seem deeper than the script, but these are plot devices, not characters.
As for the plot, by far the most interesting thing about it is the twist, which happens too late in the movie for much fun to be had with it. And after Ivy gets help for Lucius, there's no satisfying conclusion. It just sort of ends. The implications of the charade ending (or attempting to keep it up) aren't explored. Personally I don't think the Redwall-villain looking monsters were particularly interesting or scary, and I think the reason so many critics hated this movie is because it was advertised like a monster flick when it wasn't.
If you want to see the promising ideas in this film fully realized, read Running Out Of Time
. I'd actually read the book before this movie was even made, and didn't learn until later about the similarities. I don't know if Shyamalan took the idea from the book or came up with the same idea on his own (which is possible), but the book does it better. The twist is revealed much earlier in the book, and get this, when the charade ends the consequences are EXPLORED. If Shyamalan WAS inspired by Running Out Of Time
he should've just made a movie of that book. He'd have had a better film. Instead he stuck to his own formula. Big twist Ending! Use color for visual themes! Did the "bad color" make any sense? Is red really the only thing that might draw people's attention to the village? Yeah, the book did it better.