I think book to movie deals are rather suspect anyway as an unwritten rule. How many classics like Wuthering Heights and Pride & Prejudice get completely mashed and overwritten in their first 'adaptations' - a much better and accurate description.

I'm thinking of the late 1930s/early 1940s starring Laurence Olivier as Heathcliff and Greer Garson as Elizabeth Bennet which are complete abortions of the books, although they're nice enough stories if you forget the originals.
To get contemporary, I'd say that possibly the earlier HP films were good examples of what's been the best transposed from page to screen, but then JKR is the ultimate doyenne of franchise milking, so there's a lesson there in that you always retain as much script and casting control as possible.
LotR is possibly a more sensible example since there was definite tweaking with the plot, but the screenplay was extremely skilful adapted and sculpted in places to mitigate some of the more disgraceful excursions, the worst of which are (arguably, but don't because we'll be here for hours - arguing

) having Arwen suddenly elevated to the numbers of the Calaquendi (the Nazgul would have minced her)

and chopping the
Scouring of the Shire out altogether - after
filming the bloody sequences and putting them (properly) in Galadriel's mirror-cum-bird-bath for the visions that were supposed to be seen by Sam (who didn't get a look in for that scene in the movie)
Sometimes it's necessary to alter swathes of pages so it doesn't get in the way of the story/dramatisation. So the Tom Bombadil part in the first part of FotR is mostly superfluous and isn't at all relevent to the core story so even most experts don't quibble too much at that part being left out (although I'd have loved to see Billy Boyd getting eaten by a tree!

).
Visuals are different I guess - words that work on the page don't always make it onto the screen so well (even with CGI being so good these days) for some reason, especially when the words are so ingrained and well-beloved by the bookworms.
