This is your run of the mill horror movie about people poking around in places they really shouldn't be going in. That said, it does have some things working for it:
- Decent cinematography - There are some well shot scenes in the catacombs and sewers that give a very claustrophobic vibe and dark foreboding atmosphere
- Good Gore - There isn't much in the way of this for the first half of the movie, but when it shows up there is plenty of it and done in a way that is believable
- Competent Acting - All of the actors knew what they were doing and conveyed the correct kind of emotions when they needed to
On the other hand, it has some stuff that undercuts it:
- Awkward Music - There are a few times throughout the film where inappropriate music suddenly comes in that really takes you out of the movie and scratch your head wondering what kind of effect they were going for here
- Weak CGI - for the most part the things using it are kept hidden or use POV which negates this, but for example a scene of someone getting blown up uses some clearly CGI'd effects. Not close to the worst I've seen, but far from the best
- Lack of Explanation - I suppose this is more of a personal opinion, but there is never a reason why or how the bad guy survived in a place like this which can be a bit irritating
- Lack of Subtitles - This applies only to the (not-French) dialogue which is never given a translation but only comes up in the very end of the movie. It isn't needed, but it can be irritating to try and figure out what the person is saying when it might illuminate their backstory somewhat
- Generic Ending - I won't go into too much detail, but yeah, this goes the route of so many other horror films, and doesn't even explain how it happened which seems like a cop-out.
Overall though, definitely worth a watch for any horror movie fan.