The Incredible Hulk is a character who has gone through his share of casting growing pains. This movie has one of his most confusing, and forgettable casting choice. For one, this movie is part of the Marvel Cinematic Universe, but much like Terrence Howard and Don Cheadle, the actor was switched to Mark Ruffalo. I don't think you'll find much useful information to help you understand the MCU in this movie though. This was still in the early phases when they were simply introducing characters.
This movie has one really great thing going for it. It's not an origin story. They show you the Hulk origin in the opening credits scene, which I had found to be very smart after having already been through the Eric Bana movie. I wish 'The Amazing Spider-man' would have made a similar choice.