The movie is extremely different from the book even though it should be a film ADAPTATION to a book. The movie disappointed me as a big fan of the Percy Jackson series, and it just feels like they didn't even read the book. I prefer to be in Tartarus near Chaos alone then watching this s**t. There are too many thing they did wrong here is a list (that could be bigger if I had more time)
1. All of the appearances of the character (Percy has green eyes, Annabeth is blonde, Grover isn't black (no racism here, just inaccuracy)
2. The quest (The pearls were a gift, no map or shield from Luke in the book, Grover should have wore the shoes)
3. Most characters were cut (Mr. D, Clarisse, Nansy Bobfat)
4. Percy and Annabeth should be 11 and not 16 (no examples here)
5. Many epic lines were changed like: you drool in your sleep
6. Messes up the underworld (entrance in the wrong place, Charon shouldnt be a ghost thing, Persephone shouldn't be in the Underworld during the summer)
7. Behaviour of characters (Grover should be scared and not confidant, Annabeth isnt just fighting all day)
8. There shouldn't be any centaurs except Chiron, they did Capture the flag wrongly
Honestly there is much more just read the books. You can see the movies but I don't highly recommend it.