These are hit and miss with me. I would say that there are some really good ones, some that are so-so, and others that are quite terrible. What makes books so hard to portray in movies?
1. Well, I would say that when we all read that we have our own imaginations along with us. Even if the author describes what the characters and setting look like we will each view them slightly differently. We also hear their voices differently. In a movie it can be so hard to fit those expectations for those of us that have read the book.
2. Then there is also the fact that most books can not possibly be shown in a two-hour period of time. Some things, like certain scenes and sometimes even characters, are completely omitted. When some of those, if not all, are dear to you then it can make you a tough critic.
3. The other issue is getting the right cast or a good cast, at least, and having the movie funded to be able to do everything that needs to be done. Now some moves can be small-budget films and still be pulled off marvelously. BBC has a bunch of these and I've seen some excellent Dickens' books and other classics pulled off really well. Of course those still had fantastic actors and crew. There are others that just can't be done right without a large budget.
A few other books that have fairly decent adaptations: Lord of the Rings trilogy, Hunger Games (don't hate me for saying this, but I actually prefer the movies to the books, all that omitted violence and tragedy), Divergent wasn't bad, and Anne of Green Gables (the first movie, except I missed the twins from the book). I was disappointed by Mortal Instruments because I felt they took out most of what made that first book good - all the conversations and witty banter - and I didn't like who was cast as Jace.
How about you? Do you have some books that you liked adapted to movies and some that you thought were not so well done?