I think I'd give this book a solid 3.5-4 stars or so? 
 I definitely enjoyed the book while I was reading it. It was a very fast-paced read and I easily could have finished it in a sitting or so. I really enjoyed the mystery aspect of it, and it kept me interested in finding out what was going to happen. Honestly, I did see quite a few of the reveals coming, but definitely not everything, so it didn't lose it's intrigue. 
 One issue I had was that the point of view switched between the two protagonists, Amy and Elder, and their voices weren't distinct enough to separate them. I also found that their relationship developed extremely quickly to a certain point, and then slowly built. I liked the slow build that was later on, but the initial jump in their relationship was a bit irritating. Otherwise, I don't think I had many more issues with it. I think I've decided I'm not the biggest sci-fi fan (in terms of books, mainly) so I was surprised to find myself not getting annoyed. 
 I liked most aspects of the ending. One thing in particular, made me really happy:(view spoiler)[ I liked how Elder was a genetic clone of the previous Eldests, and how he didn't know if the ship could really survive without using that drug thing and him considering ruling like the previous leaers did. I didn't like his thoughts or the idea of the using that drug thing (I can't remember what it was called!), but it made sense and I thought that it was quite smart of the author. (hide spoiler)] 
 That being said, I don't think it was a particularly outstanding book. After finishing the book and reflecting back on it, I feel a bit "meh" about it. Definitely wasn't bad though. Yeah I guess 3.5-4. When reading it, I felt it was a 4, but I feel like it won't leave a lasting impression and I may forget about it in a couple weeks.