4 stars is a pretty good rating, it's funny though that big lovers of this book may be disappointed in this rating, I've got a small unpopular opinion.
I really loved this book. It's definitely one of the most unique YA books I've ever read. The Raven Boys made me feel everything, happiness, sadness, fear, anger, etc. And it's rare to find a book that will do that. I'm totally hooked on this series, and I'm happy to be, because Stiefvater manages to not waste a single word, they all contribute to a well thought out plot. I also LOVED the characters. Every. Single. One. They were so well written, and each one held their own significance, even if they don't seem to at first.
This book definitely isn't for everyone. I can say with confidence that if you don't like other paranormal books like The Unbecoming of Mara Dyer, you won't like this one. And if you have a hard time with books that don't jump into conflict right away, you won't be able to get through the first 100 pages of this. (side note: I think that's totally okay, everyone has difference taste in books).
The reason this got a 4/5 and not a 5/5 from me is that for while, I didn't care at all what was going to happen to the characters. I found that, because their backstories aren't revealed early on, it made it feel like just another book despite the intriguing plot. I have confidence that I'll enjoy the other books more, because going into those, I'll already know the characters and what they're like.
As well, I think the hype was just a bit too much. Like the Throne of Glass series (for me), the first book felt so hyped up by the people who love it and can't stop talking about it, it made me go in with super high expectations and no book can live up to.