There are so many reasons as to why the movie is just about the worst adaptation I've ever seen. But as a very devoted part of the Rick Riordan fandom, perhaps the most disappointing thing about this movie is the fact the about 10% actually matches the beautifully described and perfectly paced events of the book.
The books feature unforgettable and hilariously iconic moments which are recalled throughout the progression of the series...which the movie does not contain.
After reaching camp half-blood, Percy is supposed to wake up to see a blonde girl leaning over him and commenting on how he drools in his sleep. This memorable moment, a favourite to many of those in the fandom, is completely cut out in the movie. While watching, I was dying to watch this play in action because I, along with practically every other member of the fandom, am a die-hard #Percabeth shipper...and then it never came.
This next detail I didn't really mind but it was key. Percy was not supposed to be all love at first sight after seeing Annabeth...oh boy, that is not it.
Also, Annabeth is supposed to have BLONDE HAIR. Not straight, reddish-brown hair. Like what the hell? How do you even mess that up?
This detail isn't just for the fandom, but just about anybody who knows the slightest bit of greek mythology: Where is Ceberus and why the hell is persephone in the underworld DURING THE GOD DAM SUMMER
And finally, How did the movie producers have the nerve to just let Percy be okay with his dad being god of the mother-flipping sea. There was practically no emotional reaction - by this I don't mean that the actor did a bad job of acting out emotions - I mean that it wasn't there at all. They completely smeared out the anger he was supposed to feel upon realizing his dad had left them with a terrible life and a stupid stepdad.
Also, where are Clarisse and Mr.D
Anyways, overall... the movie was a super massive letdown and my personal advice to people interested in watching the movies, don't. Grab your copies of the movies and throw them into the deepest, darkest pits of Tartarus, go back to your house, grab a mug of hot cocoa with extra marshmallows and whipped cream and curl up in your bed with your glorious and holy copies of the lightning thief BOOK.