I loved seeing the way that Maas combined aspects of Beauty and the Beast, East of the Sun/West of the Moon and TamLin, three fairy tales that are very similar but each have unique aspects. The worldbuilding was strong, though a little more clarification on how the land worked and related to other continents would have been nice. 
 Feyre as a character has strengths and weaknesses. She demonstrates well the difference between being intelligent and being informed. She has mostly good reasoning skills (yet it took her forever to figure out a riddle that I immediately guessed the answer too), but still took time to think things over. 
 As noted above, the riddle bothered me. I understand that had she solved the riddle right away the book would have ended much too quickly, and we would have felt cheated of the trials, but my goodness that riddle could have been a little more challenging.