I saw it at a timeout screening a couple of months ago and loved it. I don't think it will be a mainstream hit, which is a great shame as it deserves to be. I wouldn't go in expecting an epic, as it was more of a thoughtful slowburner.
The trailer reminds me of 2046's trailer, which gave the impression that a lot of the film takes place in the futuristic '2046'. Similarly with Franklyn, Meanwhile city, feature less in the film than I expected, but I think for the story, the balance was just right. It's a refreshing British film, I wish more films like this would be made! Go see it!!