I read The Girl of Fire & Thorns in May and then The Crown of Embers in September. I must say that I'm quite proud of myself for reading this entire series in one year!
Judith @ Paper Riot posted this great post last week about her enthusiasm diminishing for certain series over time, and I have to agree with what she wrote. I think this is why I have such a problem with finishing series; I read book one and I'm all "This is AMAZING! I can't wait for the next book!" and then by the time the next book comes out, I'm just "Meh. I want to read something else." BUT with this series, I gobbled up book one, waited for book two to come in at the library, and by the time that one was finished I didn't have long to wait until book three came in. I think it also really helped that my memory was so fresh on the storyline too. I have a tendency to be really forgetful with books and I think I don't finish series specifically because I just can't remember what happened in the first book, nor do I have that sense of urgency that comes just after I've finished reading the book.
BUT I digress. I have to say that I still liked The Crown of Embers a little bit more, but this was a fitting end to the series. There was one part that I still don't think I really understand. Just in case I'm being spoilery, if you've read this (highlight the next part) -- what was up with the oasis? I think I need someone to e-mail me and help me make sense of that part. I'm a little confused.
I recommend this series wholeheartedly. It's a great story, fantastic world building, characters that are really well developed and an interesting premise.