I have been highly anticipating this book since I read A Court of Thorns & Roses​ last summer! Let me just start by saying it was worth the wait! Ten fold!
A Court of Mist & Fury picks up where ACOTAR left off. Feyre has defeated the villain Amarantha, thus freeing the Fae of Prythian from her reign. She goes back with Tamlin, the Spring Court's High Lord, whom she loves. Now that Feyre is a Fae herself, she struggles with fitting into this new world, as well as helping rebuild it. She struggles with the darkness she faced Under the Mountain, but is trying to build a life with Tamlin. However the deal she made with the Night Court's High Lord, Rhysand, looms over her head... one week a month with him for his help during Amarantha's tests. Not only that, but the threat of war is brooing. 
Sarah J. Maas does a great job of bringing our beloved characters back for an even better story than the first. While ACOTAR was a Beauty & the Beast retelling, this follows the darker story of Hades & Persephone. For those of you that aren't familiar with that story, I highly suggest reading it!