The first book I've read in German! I'm so proud of myself for reading it all, even though I didn't understand 100% of it.
Anyway, I found the book to be very realistic, and it hit uncomfortably close to home at first. I've never had serious issues with my weight, but I have been an outsider in my class, and Eva's coping mechanisms were very familiar to me. I disliked the way that subplot was handled, though - having everyone else actually like the main character and be friendly with her as soon as she put in some effort is both overdone and can be very damaging, because it is rarely true in real life.
I think that the part with Michel was done well - he was far from a perfect boyfriend and had quite a few problems, but he was trying, and he really cared about Eva quite a bit. I enjoyed how it was both kept realistic - your first boyfriend being awesomeness incarnate is unlikely, especially if you don't know what you're looking for yet - while still showing that yes, you can have a boyfriend that likes you for you, while still seeing the parts of you that you dislike.
As I said, I've never had problems with my weight, so I don't think I'm qualified to talk about how well/realistically that part was written, but I loved the message that the key is in moderation, and that starving yourself is not the answer.
Overall, I quite liked the book and thought it had a very real voice (well, as far as I could understand - the slang is probably quite outdated, for one). I think it touched on a lot of big problems for teenagers, and did so in a way that was both respectful and genuine. That being said, people who have had problems similar to those of the main character should keep in mind that the book is at times incredibly direct and brutal and can potentially be triggering.