Being a big fan of the book (one of the very, very few I've read twice), it was fairly enjoyable seeing the gist of it in the movie.
This was the directorial debut for Matthew Lopez--prior to this he'd only been a playwright--and, to be blunt, it shows that this was his first time, at directing that is, hehe.
Perez is certainly the epitome of eye candy, and he did a good job at portraying the character's cocky personality from the book. Galatzine is handsome enough to be eminently kissable but not a match for Perez when the clothes come off (although I wouldn't kick him out of bed for eating crackers). I think he also caught his character's personality from the book pretty well.
The pre-release publicity waxed euphoric over the "chemistry" between the two leads. While they were pretty much perfectly cast when it came to how I imagined their looks from the book (although the prince was supposed to be the taller one), I thought the chemistry was at best intermittent. The museum scene was a perfect example, part of it worked, but overall it didn't.
The pre-release publicity also trumpeted how the R rating meant that the book's steaminess--they basically sucked and fucked all over the globe in the book--was going to end up on screen, but, compared to the book, it was waaay watered down, barely more than "fade to black".
I actually thought the first anal scene was fairly realistic. It was the fist time for Perez's character, and those first times are very often awkward, as anybody who's ever done it can tell you.
Sarah Shahi as Zahra Bankston (POTUS's chief of staff) was awesome. Nobody else really shone.