This movie is quite up to the standard of fast moving original horror flicks made after 2000! Also the fans who don't like suspense there is enough gore to keep you entertained. The story (only female leads) is quite gripping. Even for the most experienced horror fan this film contains twists you cannot expect.
The only real problem I have is that the female characters are not very likable. I didn't have much sympathy for them. Some of the actions of these characters are very questionable and seemed to be aimed to shock rather than compel. You just don't care that something will happen to them. I also had trouble relating to their hobby. What possesses people to go adventuring deep into caves they know nothing about. Especially if the rest of the world is unaware of this. Surely you take some precautions in case things go badly. None of that here. How often don´t you read about incidents where people get lost or killed because of an adventure go wrong or where others have to risk their lives to save these imbeciles. It is hard to evoke sympathy for people who disregard safety like this but at the same time expect to be rescued when things go wrong.
That being said however there are some very good old school horror elements that make up for most of the flaws. The setting, the darkness and the sound are very effective. You can imagine the terror the characters must be experiencing. How would you carry yourself in a similar situation? Another solid entry coming from Neil Marshall. It´s been a while he has made a movie but here is hoping he will come back with a vengeance.