Earlier today I finished reading Limitless by Alan Glynn. It's an fascinating premise and I enjoyed the book. The interesting, and sometimes confusing, thing is that Alan Glynn is a British author living in Dublin. But his book has American characters, is set in New York City and uses US English, except for a few discrepancies. These are more editorial annoyances than anything. I love the literary references.
I just watched the movie and was struck by the largest UK/US cultural difference. While the book ends with a more realistic outcome, the movie follows the American Dream formula. In the US we like the myth that anyone can pull themselves up by their bootstraps, become wildly successful, all based on hard work and a bit of talent. In England they have centuries of reality and class system and no such cultural fable. As always with a book, there are layers of meaning and many details that weren't in the movie.
Honestly, I preferred the movie. The details in the book were great, and I very much enjoyed reading the book. The movie conveys the feel and mood better, and I am a sucker for a good happy ending. Having read the book, it gave some great background to the film. I'd suggest reading the book before the movie if you are so inclined.