First of all, people need to stop saying this is an interpretation of the novel Frankenstein by Mary Shelly. It is anything but that. This story takes place about 10 years after that novel was published, which was my first clue that this was going to be something completely different. As a nice early surprise, the novel itself does exists in this tale, which adds further realism to the whole affair. What this tale is though, is two things. First, it's a superb detective mystery. Secondly, it is well-executed, well built-up, gut wrenching horror.
The premise is undeniably very dark, and ingrained in the times, but there are underlying themes that are quite relevant to the world of today--it is a mirror for certain scientific dilemmas of 2015. The protagonist (played by Sean Bean) is a good man but a tortured soul, with high potential for being of unreliable perspective (his character might be experiencing dementia). So that alone will keep you guessing. If you start watching it, watch it to the end. You will see that it is anything but an interpretation of the novel, Frankenstein.