Lack of Mystery and Puzzle Solving...
Compared to previous two Langdon movies this was more action-oriented rather than mysterious and investigative. Having read the book before, I felt like watching a James Bond movie.
The reason I loved previous Langdon movies is that feel they have, an overall theme. I thought it was lost here.
Also, the movie was really fast. There was no many intriguing moments about art pieces and historical facts.
And I don't get why they changed Sienna's character to some obsessive psychopath woman, and created romantic storyline between Sinskey and Langdon. But (besides these changes) it still would be better movie, only if they could slow it down a little and include more (and longer) scenes about mysterious symbolism (like in the book).