I read The Count of Monte Cristo last year and happened to catch the 2002 film adaptation on TV earlier this month. I'd seen the movie in theaters but I'm pretty sure I hadn't seen it since, though I remember liking it when it came out. Now I'm less sure how I feel about it.
The book is incredibly long - probably too long. It wants to do a lot of things in a really brilliant way but has to settle for doing a couple of things brilliantly and the rest of the things in kind of shitty way. The Carnival section is much too long, there's a tremendous amount of backstory on several characters who don't actually have much of an impact on the novel, and the length of the damn thing eventually makes its protagonist less sympathetic than he would be in a shorter story.
The 2002 adaptation solves a lot of these problems by dropping all but a few characters and cutting the story down to a manageable size (and almost completely ditches Carnival, which is a SIGNIFICANT improvement). But it also loses a lot of what is interesting about the novel from a historical fiction perspective, to the point that the shifting political sands that define the book become a single-scene plot point at the beginning of the movie and basically never get mentioned again. It's a tradeoff that I think makes sense from a cinematic perspective but that does make the whole less compelling - perhaps a miniseries or a TV show would be a better way to make The Count of Monte Cristo come alive on a screen than a feature-length film was.
There are a couple of changes that I think were really well done, especially in respect to the choices and agency of Mercedes. I'm never ever going to bitch that we get a soppy happy ending if that soppy happy ending replaces a master-slave/owner-lover/whatever gross relationship. The ending of the book is pretty fucked up and I think the movie did a really decent job of keeping the fucked-up revenge fantasy without completely alienating the audience from Edmond's character by having him sail off into the sunset with a brainwashed slave-girl.
The movie is a fine way to spend a couple of hours, the book is a fine way to spend a couple of weeks. One is not a brilliant reflection of the other, but it's a totally decent translation to a totally different medium.