Sometimes when actors play a part in writing a movie that they know they will be acting in they spend too much time trying to give their character room to flourish and not enough time on making the rest of the film sustainable. I think that is a little bit of what happened here. Lead actress Natalie Dormer co-wrote the movie with her husband (who also directed the film) and it has to be said she turns in a very impressive performance as a blind woman. The rest of the movie though leaves a lot to be desired.
The biggest problem is has is that it's over-complicated. Many previous films have fallen into the trap of over-complication and it has almost always harmed them. Unless you are Christopher Nolan who seems to be able to simplify even the most complex of storylines, you really shouldn't try too hard in that respect. 'Ocean's Twelve' was a prime example of that. It got so complicated that it was no longer fun. 'In Darkness' is very similar. You're working so hard to keep up with everything that you're never actually able to just sit back and enjoy yourself.
The movie is made with some nice style and I liked the amount of ambition that went into it. It wasn't done on the cheap and nasty, that's for sure. Unfortunately though it just didn't really work for me. It tried to have some "knock your socks off" moments but none of them really landed and the end result was a pretty forgettable film.