The first three books had me so hooked, that this one was a let down as much as I hate to say it. Starting with what I didn't like, as others have said, it really lacks substance and feels like a christmas special slapped in between the third and fifth book. Since there's so much action in this series, I do love a break every now and then where the characters are just living their every day lives and interacting with one another in a normal way. But I really felt this one missed the mark and I am not a big fan of it switching POV between Feyre, Rhysand, Cassian, and Mor, with Mor's parts being extra boring. In my personal opinion, I think having Rhys's POV spoils it for me a little as well, since the style in which things are described are near identical to Feyre's POV and so it somehow takes the mystery of him away a little but also feels too feminine to be his POV as well at times, with a lot of unnecessary description, such as Azriel's hazel eyes and things alike. Lots of reiterating things we already know via the previous books.
Things I did like, would be that toward the end we finally get the much anticipated "hey, war is over let's make a baby" scene which I was excited about and am looking forward to reading the 5th book to see how that develops. There are also some really cute scenes and funny exchanges amongst the characters that I thought were quite clever and humorous.
Overall, it gave me a laugh here and there but took me twice as long to read this book which is tiny in comparison to the three before it which I binged in mere days, and I actually found myself skipping some pages. I think it's important to note the author mentioned in acknowledgements that she had a lot going on while she was writing this so no doubt that may have had an impact.