There are a lot of (key) elements in the novel that were omitted in the movie, not to mention the unnecessary action-movie-kind-of-stunts that were wrapping the end of the movie. I also agree that there were too much more violence in the movie compared to the novel. The only notable deaths were one of Zobrist's at the beginning of the novel and that of Vayentha when she fell off the THIN layer of canvas (memory reserves) at the hall of five hundred.
They also disregard Sinskey's (presumably visually awesome) pendant and the fact that she was fertile and totally unrelated to Langdon and instead replaced it with an 'ex-lovers' reunion at an unlikely situation'.
Also the Ferris part, I recall there was rashes or allergy at the novel, but could not remember it until they changed it where Langdon has noticeable and worrying rashes, and was ultimately reminded that it was in fact Ferris who had the rashes. Also they replace the intriguing 'lovers moments' of Zobrist with unidentified person (it perceives me into thinking that Zobrist's lover was Ferris, while it's actually Sienna).
And to add it up, the fact that Sienna was actually bald and had a complex past, was nowhere in the movie, also, she did not die in the novel.
All in all, movie adaptations will always be inferior to orignal sources, but changing the decisive ending, really? This indirectly confirms that there won't be any sequel to the movie if the novel (hopefully) gets one due to that different ending.