I wrote a massive review for this book and it didn't post (GRRRR). So I'm just going to write a short simplified version. 
 I'll give this book 3.5/5. 
 Positives: 
 - Good introduction to the world, really interesting concept that ends up being so much more than an assassin and the competition (which is still really interesting!). The story begins to involve magic and royalty/politics/rebellion and also has a somewhat mystery/whodunnit thing. I liked the characters' names and the cities' names and one of my favourite things about the book was how magic was interwoven in the story. 
 - Strong minor characters: Kaltain, Nehemia, the King and Chaol. 
 - Some really funny scenes! Some fun banter between characters, and good developing friendships. 
 - For the most part I liked the writing (ignoring some really cringe-worthy cliche lines... mainly due to the romance, which I'll get into later) 
 - Easy, quick read 
 Negatives 
 - The romance. I found the love triangle a bit forced and it really took away from the story. So many of the challenges involved in becoming the King's personal assassin/champion were glanced over in favour of much weaker love triangle scenes and it really took away from the novel. I thought Chaol and Celeana's relationship built nicely and their scenes together were decent. Dorian and Celeana's relationship was really fluffy, and definitely was cute at times but really walked a fine line between fun and cheesy and it did drift more towards the cheesy/cliche'd side often. 
 - Dorian's character was pretty weak. I felt that his feelings were always shown directly - I found that I didn't really want or need to learn more about him, it was obvious who he was from the get go with little actual characterisation. He was a bit of a cookie cutter character, and I wish there was more to him. 
 - I feel like there was a lot of telling and less showing. The whole book concentrates on how Celeana is a badass and the best assassin. I won't deny that she does kick butt and with style, but I found myself doubting whether she actually was the best assassin when we didn't really get to witness so many of the challenges in the King's competition. 
 - Celeana was a bit mary sue at times - it seemed like she could do anything, and everyone loved her. She was stunningly beautiful, intelligent, musically-talented, physically a badass, etc. etc. I don't think I remember a single thing in the book she could not do or struggled with. I did like that we did get descriptions of her flaws (aggression, arrogance) which were really entertaining to watch but I did hope this would be more fleshed out. 
 Despite everything, I liked the book. It was fun. At times it frustrated me but I am definitely interested in the world and story that Sarah J Maas has created.