This film has amazing potential including the mysterious underground catacombs of Paris, a rave in the crypts, weirdos galore including the lead -- even a goat monster on the prowl. Unfortunately, while it offers some entertainment value, it devolves into a jumble of underground in the dark shots that are not patched together well, and in the end, nothing much to take it beyond the potential and into the realm of a good movie.
With hundreds of miles of catacombs to play with you would think they could have dreamed up some interesting places to stop. Maybe the Nazi bunker which is down there would have added some creep. Or a secret meeting place of a cult. An old crazy recluse. I mean, something more than endless stairs and passageways and pools of water and places that look like the attic of an old house in need of a rummage sale. There's just nothing to make you go "Wow!" or prickle the hairs on the back of your neck.
It doesn't help that the attractive lead is an asexual emo queen. Sure, she's been through a lot, but most of her actions consist of screaming and running, followed by more screaming and running, topped off by more screaming and running. By the end she is thoroughly unlikeable mess with no real redeeming qualities, and that's before the real "end" which I won't spoil here.
Actually the best part of the movie was the flashlight. To steal a line from Will Smith: "I have GOT'S to get me one of those." Not only does it last forever, and display immunity to immersion in water, it survives falling ~100 feet onto hard concrete and doesn't lose a lumen in the process. Hmmm. The fact that the flashlight steals the show says something about this movie. Not a bad movie. Just not a good one.