Despite the strong start, and great performance of Tom Hardy, the rest of the movie falls short.
(spoilers ahead)
The movie starts off introducing you to the Kray twins; gangsters who are respected and feared. One of the Krays is unhinged and erratic (Ron), the other is charming, cunning and ruthless (Reg). You are also introduced to a detective who is hell-bent on ending them both. Reg is a very likeable character, and in the beginning starts a Romeo and Juliet-like romance with a girl he apparently knew as a child. There's an excellent fight scene towards the beginning as well.
The problems lie with the character/story development of almost EVERYTHING that isn't directly related to the Krays. You barely know who Reg's love interest is, and are given no reason to get attached to her or like her. You have nothing to go on with the detective who's name I can't even remember, besides the fact that he hates the Krays. You are given barely any insight into the rival gang. And the mafia who skips across the pond to do business with the Krays is given one ambassador to the audience, who I believe is in a grand total of two short scenes.
Everything else about the movie is a haphazard mess of "plot twists" and bad story-telling. The biggest gripe in this department is the out of pocket rape committed by Reg, which is COMPLETELY out of character. He may be a gangster, but for 99% of the movie, he is respectful to all who aren't opposing him; especially women.
I love Tom Hardy, and he did carry the movie, but it wasn't nearly enough. Biggest waste of 2 hours in a very long time.