Let's get one thing sure from the start. The Descent sequel is ten times better than most of the horror $hit that gets churned out nowadays. Unfortunately though, much like a new recipe for Blackthorn, it's just not required.
Neil Marshall's original was a complete movie. It had the lot. A great cast, a great story, a claustrophobic setting, a truly terrifying horror movie. What it didn't require was a sequel. The directors vision ended, completed, finished, story over. The Descent in all its glory was Marshall's masterpiece. Alas, success and the US ending paved the way for the sequel......
...You see, for those of you that have seen the original, In the US it ended at the Jump sequence in the car. The classic standard affair, Carrie, Elm Street, Event Horizon et al horror movie underpants changing ending. Hence the missing of the real depth and undertone of the story and the green light for franchise.
So on a pure horror movie experience the sequel works. It's pulled to together pretty much the whole team (director aside) and returned to the settings of the original. It kicks off from where the original ended in the US and it brings the same style of pure terror that the original did. Unfortunately though, it lacks the characterisation and depth of the original and works pretty much on a base horror level. Which means a lot of gore and a lot of jumps.
So if you can ignore the cheesy 'Hell itself' line, ignore the fact that two slightly overweight members of the local sheriffs department can cope in this unexplored cave system, ignore the terrible ending and are happy to watch a watered down version of the original then you will love this. I can only hope that if they are thinking of making another one, that they go down the route of a Cameron's Aliens to Scott's Alien sequel. Otherwise they will be hammering a classic into the depths.