The Count of Monte Cristo will always hold a special place in my heart because I read it as a kid and it was the first real "grown up book" I ever read, and it absolutely hooked me. I was reading it under the covers with a flashlight when I was supposed to be asleep. It has the vivid, detailed descriptions you find in the classics, but without slowing down the pace. There's a bunch of different threads and subplots to follow, and I generally feel like most adaptations don't do it justice, because it takes more than a movie or miniseries to tell the story - the one exception being Gankatsuo (as mentioned here already) which changes the setting but follows the story pretty faithfully, giving it a full season and starting midway through.
On top of the action, adventure, and schemes, it also has social commentary, philosophy, and interesting characters. The count occupies this unique position in the upper class in that he's not old money and not tied to the aristocracy, but not exactly new money either, in that he's not a merchant or capitalist. He's just this free agent with his own agenda and values, and nobody knows what to make of him.
It's fun, it's very thought-provoking, and the imagery is striking. Big fan.
It's a bit of a leap, but I think there's some similarities with another one of my favorites, Crime and Punishment. In fact, looking back at what I wrote, "On top of the action, adventure, and schemes, it also has social commentary, philosophy, and interesting characters" is exactly on point for it too. It feels more modern that the era it was written, I've seen it described as a thriller and I think that fits.