Well this is a difficult one to rate & review! But finally I am just glad to have read Fourth Wing after the hype. 
So positives first, this is such a readable book, it is fun, engaging, difficult to put down even with the page length. I think this is what makes this so popular, I really enjoyed the plot and magic in this world, it isn't particularly original but it worked well together and it was paced well. For the most part I also enjoyed the characters, the side characters are good if a bit underdeveloped, but the main characters have enough depth and the romance between Violet and Xaden I thought was at least successful. I prefer Xaden a lot more to Violet personally.
For me, what let this book down was actually the writing, it felt very novice but perhaps this is because it's first person from Violet's POV. Violet read as very young and not very mature, I wouldn't say she was a typical 20 year old. Also I'm not offended by the foul language, but the overuse of the F-bomb was too much for me, it was used as a crutch. There also is plot holes and a lot of unfinished storylines. I found that the writing was choppy in places where the timeline was cut and merged back together.
It ends with a cliffhanger which I knew going into it and now I have Iron Flame to continue with the story. I am hoping the writing improves for book 2 but for the most part it is an enjoyable read if you don't go into it too critically. 
3 stars