When Hulk is in focus, for the most part, he's the purest adaptation of what Hulk was in the comics. His powers were the same for instance and his backstory was there properly (more of which later), but he is conspicuously in short supply despite this being his own movie.
Because Lee chose to elevate a backstory to the main story, there's just not enough room for the title character, which is a fatal crime.
We spend way too much time looking at David Banner's research and following him trying to reveal himself to his son, and on examining the theory of Banner's repressed emotions rather than on the results. So those results - or Hulk, as he's known - ends up being a side-attraction in his own circus.