I almost never come across a bad review of this book, and I don't understand how that's possible. It's not that Throne of Glass is terrible--it's just that there's absolutely nothing remarkable about it.
If anything, Throne of Glass is a wasted opportunity. It's a book about a freaking assassin! I mean, think of all the possibilities! Think of what kind of morally ambiguous and conflicting story you could write with such a protagonist! Unfortunately, Sarah J. Maas is apparently intent on making you forget that Celaena used to be an assassin. For those of you who don't know (the author may or may not be among you), assassins kill people for money. Who did Celaena kill? Were they nobility? Merchants? Peasants? Cheating husbands? Did they fight back? Beg for their lives? Did Celaena feel any remorse about killing them? I have no fucking clue. The story never names a single one of her victims. Sure, there are a couple of vague references to remembering her first kill, but that's about the extent of it--we never get any details. And sure, I suppose I could read the prequels to find out, but a) I have no motivation to do so, and b) I shouldn't have to. This element of Celaena's past is central to her character, so why isn't any of this in the book?
There are several occasions where Celaena remembers other people doing horrible things to her, but what about all those times where it was the other way around? It's almost as if the Sarah J. Maas were afraid to let readers dislike her precious Mary Sue* protagonist. NEWSFLASH, AUTHOR: You cannot write about an assassin and then not let her get her hands dirty!
But anyway, going back to the whole moral ambiguity thing: This book doesn't have it. I can very clearly draw a line separating the "good guys" and the "bad guys". (In fact, the gap between those two groups is so large that I could probably draw that line blindfolded.) Sure, some of the "good guys" have flaws, which is why this novel isn't a complete fail (that, and Nehemia), but they still fit very neatly into the "good guy" box.
Aside from that, this novel has a number of other problems. Most of them are plot and character-centered. Let's start with the plot as a whole: a group of criminals are competing to be the king's Champion. If you were a king and you needed a champion, who would you pick? Personally, I would choose from the ranks of my best soldiers--people who have fought loyally for me and who will continue to do so. I would not pick a criminal. Criminals tend to be selfish and unpredictable. If I don't even trust an individual to compete in a tournament without leg irons, why would I give this person a weapon and expect him or her to take orders from me? That's not even the only instance of something that didn't make any sense, but I'm getting tired of writing this, so I'll just end it here.
So in short, this is the most overrated book I've ever read.
*Yes, Celaena has flaws (arrogance and immaturity), but all of that is overshadowed by her special snowflake status. She's the most famous assassin in the whole kingdom, she's beautiful even after wasting away in the mines for a year, the boys are obsessed with her, and she even gets a bit of "Chosen One" status. Plus, that hideous spelling of her name. I don't usually use the word "Mary Sue," but in this case, I'm calling it. She's a Mary Sue.