I know that it’s not possible to fully adapt a book into a film and some artist license has to be taken but sometimes it’s good and some times its bad. So let this be a place to spread your praise or dump your salt!
So for example in the Favourite Fantasy Novels thread we have been talking about the Artemis fowl series and it’s questionable film adaptation. In contrast there’s the Mortal Engines series which seems to have been successfully adapted into a film.
Oh yeah… When it comes to disappointing book movies, both of the Percy Jackson movies come to mind… Personally I think the first movie is mediocre… As a movie on its own. As is the second one. But they don’t work together, and if you’ve got any fondness for the books at all you might as well not watch them. I have a similar feeling about the Eragon movie too, y’know?
Coraline was an amazing movie based on a book, but it definitely diverted a whole lot from the original book… Probably for the best, or I feel like it would have traumatised a generation haha 
If I remember rightly Rick Riordan just point blank refuses to acknowledge that the film’s even exist 
The problem with the film’s for me is that they complete throw the entire story out of the window by making him sixteen in the first film. The books completely revolve around the whole when he turns sixteen prophecy
Then in the second film they mess around with the golden fleece and it temporarily bringing back Kronos when that didn’t happen at all! They also missed out the funniest bit from the ending which was the canaible sheep!
And also the Guinea pig nonsense!
(As a massive fan of the books I have a lot of salt about the film’s 
)
I was so glad that there was maybe one other person way in the back of the theater when my friends and I went to see Lightning Thief. We were closer to the front nitpicking everything. Key among them, of course, that you can’t change character ages and not change the super important plot device that’s age specific. 
I’ll be back with some that I think did a good job. The only thing I can think of at the moment is LotR (Peter Jackson’s, of course, I’ve only seen the first half of the older animated one, which I found painful, mainly [spoiler]the replacing-Glorfindel-with-Legolas-he-has-no-reason-to-be-on-that-side-of-Rivendell-at-that-point-check-the-map-at-the-front 
[/spoiler]…I have feelings about this).
I actually prefer the LotR film’s over the books as oh my gosh there is so much damn walking in the books!!! Though they do miss out the very important character of tom bombadil!
Also I’ve just thought of another series that I despise My all time hated series is A series of Unfortunate Events! It took me over 11 years to read those awful books and I’m so glad Netflix made an awesome TV adaptation! Though the end was lack luster unfortunately missing out some really important and moving parts from the books
Oh yeah @Ashburn , the LoTR movies and the Hobbit movies are fantastic! Absolutely classic, basically laid the groundwork for high fantasy movies from then on (for better or for worse…)! Long, yes, but I think it took exactly as much time as it needed to.
And @Rimor I agree… I could never get through those books, the language was clunky and the pacing was confusing… I actually really liked the movie tbh, it condensed a good sized amount into an enjoyable and visually interesting experience. The scene in the car and the house on the cliff absolutely changed me as a kid, I’d say. I haven’t yet seen the TV series, but I hear good things! And from reliable sources too, so I’m inclined to trust them 
Definitely watch Netflix’s adaptation it is absolutely fantastic and has an awesome intro song that is still stick in my head Also Neil Patrick Harris could easily rival Jim Carrey’s Count Olaf! Though Jim Carrey did probably the truest version of him possible and it’s a shame the film’s were never finished. Like seriously he had all the mannerisms down and he just felt right but Neil definitely puts up a good challenge to the crown.
Oh and finally Patrick Warburton actually makes Lemony Snickets ramblings and nonsense enjoyable!
I definitely appreciated PJ adding women doing things in The Hobbit. I’d read it before the first installment came out and it was all men all the time. One of the reasons I was less salty about Arwen taking Glorfindel’s place in Fellowship.
I felt some of the battles in the Hobbit weren’t as good as those in the Hobbit books (Like the battle of the 5 armies) or those in the LotR film’s. However they did bits of the battle with the dragon in the lonely mountain better!
Also those damn ex machina eagles really annoy me in the films. They’re basically used by the film makers to yada yada the plot along when the eagles played a massive role in the book
I believe they actually spoke with the eagles in the book too if I remember correctly, in the movie the eagles just drop them off and go about their way. The eagles are supposed to be very proud and they were hesitant to take them as far as they did, the movie doesn’t explain why they didn’t just take them all the way to the mountain.
The LOTR & Hobbit movies we’re definitely fantastic! Though you’re right @Rimor @BrokenVoid they definitely needed to explain some plot points better - namely why the eagles didn’t take them as far as the mountain (which was addressed in the hilarious hishe video on YouTube).
A series of unfortunate events on Netflix is definitely a really good show! I love it so much but I’m still on season 2 so please no spoilers 
What did everyone think of the Chronicles of Narnia compared to the three books that they actually adapted?
I’m just miffed every time when they fail to adapt the real first book, The Magician’s Nephew.
Other than that, I haven’t had a chance to watch the newest ones after Lion, Witch & Wardrobe.
Yeah I get that, but the movies were pretty well adapted in my opinion. They stuck with main plot lines & kept the themes of the book in the movies as well which was really nice to see, even if they only focused on three of the seven books
Not technically a film.
But IMO Good Omens by Terry Pratchett and Neil Gaiman, was a book lovers perfect transition to TV. Only 1 casting that I really didn’t like, and the additional content added rather than replaced. What they left out was reasonable and didnt take away from the story, although would have been epic.
Netflix Series Of Unfortunate Events did a very good job capturing the writing style from the books. Certainly a lot easier to watch than to read.
Twilight, yes I’ve gone there because I find it hysterical. It’s the only book to film I know where they had to invent content, because the book included as a whole was insufficient to make a full length film.
The trailer for BBC His Dark Materials looks promising, not too sure about some of the casting, but others they have got perfect. I’m eagerly anticipating this one 
I really enjoyed Mortal Instruments, I was disappointed when they didn’t continue with them. I also watched the tv series on Netflix, it strayed far from the books but if you’d never read them I could see why people would like it.
So I’ve just watched divergence and it’s absolutely awful compared to the books The film industry seems to have had a really hard time converting trilogies like Hunger games, divergent and 5th wave into good films series
I really enjoyed Good Omens as well! I think they did a really good job adapting it. I know there was some upset over the casting and some roles, but I rather enjoyed the whole thing.
Also, I’m the biggest Pratchett fan, so I’m just biased to like his stuff. Even the old Hogfather film is good in my eyes, and I can’t wait for the Watch TV show.
Oh, the Watch books are my favourites! I read them a lot as a kid. For some reason they were the only ones I read at the time even though I generally dislike anything to do with police. Terry Pratchett had an amazing way with words, I hope they can make something powerful from what he’s gifted the world!
The old Dresden TV show is a fav of my mum, she loves it. I just was too young and too easily scared to enjoy it when I tried watching it… Especially since the first episode I saw was the skin-stealer one. Scary…
@Cirydae I thought I was the only person other than my husband whose excited about the Watch series 
I can’t believe how much I miss Discworld. 
On the subject of books to film, I was most disappointed by the lack of subtlety that can often happen with the adaptation, like the last few Potter movies. I appreciate that you can’t adapt everything, but I do like a political subplot.
So Disney.