Cons: They changed the character's up from 12 to 16, All the actors do not match their characters, (Percy's described as having Black hair and Green eyes, Annabeth is Blond, and Grover... ugh. Complete change. He's white, not black! Not to sound racist, but I hate it when they change the books so much! And Grover is now cocky and flirty instead of cowardly, yet dependable and loyal, which I loved!), complete story change, (It was Percy's mom who stayed in the Underworld, not Grover, Annabeth doesn't go up to Olympus with him, the only gods in the throne room are Zeus and Poseidon, not all fo them, Hades isn't evil, Luke is acting on his own, no Kronos, etc. Oh, and no mention of Luke and Annabeth's past.) The fact Thalia's back story is shoved into a deleted scene, the lack of Clarisse, one of my favourite characters, (both these are getting fixed in the next film, thank the gods!), the Lotus Casino and Medusa scenes, while still in the movie, are completely changed, they basically canon raped the whole book, the lack of many book moments, not much foreshadowing to the upcoming books, Thalia's Pine Tree is nowhere in sight, just gone, and magically appears in the next film, and if it is, it isn't pointed out, the general lack of most of the Book's plot, the lack of Percabeth. And Hestia's cameo is cut. I loved that part. It foreshadows the last bit.
I mean a good amount of the books are description! It's the perfect book too adapt, I mean it could easily be adapted. And yet they f*cked it up. And Rick Riordan didn't read the script, because he thought it'd change his views on the characters. I wish he did. He could've set them right.
Pros: It's full of action. Mindless action. Dionysus is gone. I hate him with a passion. But nope. He magically reappears in the next one.