I had the same issue with the second book. I found the first half of the book quite boring, having to force myself to pick it up every once in a while and then BOOM, everything happens at the same time and you just can't put the book down until you finish it, and even then, you wish it didn't have to end.
It's hard to review the third and final book in a saga without giving away some spoilers, so I'm just going to say that although there were a few narrative threads that seemed unnecessary for my taste, I really liked the book, and I loved how Laini Taylor managed to bring it all to a close, making you sad and happy and, in the end, so sorry to let go of Akiva, Karou, Zuzana, Mik, Liraz, Ziri and Issa. This was a wonderful end for the series, so I'll give it four stars!
[I'm counting this for the letter D in the 2014 Alphabet Soup Reading Challenge ]