The Descent: Part 2 picks up immediately after The Decent left off, with Sarah just having survived the cave system. She later has to return against her will with the police and other people to find her friends.
If you have seen the first movie, you already know what is going to happen. They did not bring anything new into the mix, but instead continued on the old blood-spattered trail and revisited old scenes and deaths. For some reason, the movie was more focused on jump scares and monster cries, when they instead could have further developed the sense of claustrophobia, darkness and loneliness that the first movie conveyed in a very interesting way.
The special effects were somewhat weird too, like no one of the crew have seen how blood looks like. The color and consistency reminded more of a can of tomato soup than blood. Other than that, most things looked about the same as the first one, but with worse feeling.
This is a classic horror sequel, just playing along with the same storyline without adding anything into the mix.