I feel that a good movie adaptation is one that understands that a novel & a film are different mediums and need to be executed differently. Some of the best adaptations for me include The Shining & its sequel Doctor Sleep, I also like The Prestige, Jaws, Harry Potter films, Slaughter House 5, Soylent Green, The Lord of the Rings films... the list goes on.
As for poor adaptations, I recently saw The Girl with all the Gifts which I felt was a bit dull
My husband (and I tend to agree with him) gives a golden vote to Clueless, which is a modern adaptation of Emma
There have been some great movie adaptations of historical novels. I must confess to a soft spot for Merchant Ivory productions of various novels (A Room With A View is probably my favourite).
Agree with the points Rob made I'm likewise fond of The Lord Of The Rings movies and also liked most of the Harry Potter series — especially HP & The Prisoner Of Azkaban, where the film successfully built on and added to the time paradox of the novel. Another successful adaptation of a huge-selling fantasy trilogy is The Hunger Games, which I felt was done very well.
Although i’ve watched all the Harry Potter films, they annoyed me because they missed out so much detail which made the books so good. I loved the Netflix series of ‘normal people’, particularly as I didn’t enjoy the book at all. Loved both the Winona Ryder version of ‘Little Women’ and the newest one. Also, ‘Sense & Sensibility’ and the Colin Firth series of ‘Pride & Prejudice’.
2015 version of "Far from the Madding Crowd" with Carey Mulligan, Matthias Schoenaerts and Michael Sheen.
"Suite Francaise" with Michelle Williams, Kirsten Scott Thomas and, once again, the swoon-worthy Matthias Schoenaerts.