Here are a couple of links to some critical analyses of the Descent. You may agree or disagree with what the authors of these analyses are saying, which is fine. Think critically about what they are saying, but they work quite well synoptically and there are some interesting alternative readings of thematic and representation issues included
You can also have a look at the Mark Kermode review, just remember that you are not writing a review yourselves! You are exploring the film for it's Britishness, genre conventions, narrative theory and representation issues.