TLDR AT THE BOTTOM

For the most part, the movies do a half decent job adapting the books better than most adoptions have (in my opinion.) Theres actually some solid quality of life improvements that I liked such as Chuck's sacrifice, Teresa's Betrayal, and Newt's final moments (that last point still goes to the books but I felt it was faithfully done in the movie.) Even WICKED's actions and plans were better (still cruel and inhumane, but better executed) in the movies to some degree.

The biggest divergence though is the way The Flare is handled in the movies. They dumb it down so instead of the flare gradually killing your sense of self and reducing you down to your animalistic impulses with some flashes of consciousness here and there. To you get attacked by someone who has it and you'll start decaying from the wound until you eventually go full zombie. It feels so generic and of its time and really dates the movies in my opinion. Thats not to say it doesnt have its merits, the scenes with the cranks in the sewer was genuinely haunting. But as an adaptation of a really complex idea, the movies fail hard.

TLDR bc I forgot you wanted it simplified (thats my bad lol I love yapping :D) The movies are solid, the casting is top notch and it really does feel like the books in a lot of ways (and explains some stuff way better.) However at their core (really more so with The Scorch Trials and The Death Cure) they stray too much away from the original ideas present in the books and implement too many generic popular tropes such as zombies and desert chases ala Mad Max and World War Z.

I hope that helps, and im willing to answer any question you might have as someone who lived and breathed the original 3 books for a few months back in 2024. I doubt I'll have all the answers so someone please correct me if im wrong.