I can honestly say that this was my favorite of The Infernal Devices series. I still do not like them as much as The Mortal Instruments, but I did enjoy this installment. 
 As I said from the very beginning, I liked both Will and Jem, so I did not have a preference as to who Tessa chose in the end. I was actually sort of "meh" about the whole romantic line of this series. In Clockwork Angel, I definitely felt the connection between Tessa and Will--mostly on Will's end--and I DO love me a broody bad boy (I cannot help it). But Jem was so incredibly sweet and patient and kind that I also really liked him too. Especially after Clockwork Prince came out and we got that whole hot bedroom scene. Woooo, Jem! ;) So, I was on the fence. 
 Yes, I am a fence-sitter when it comes to this series. 
 I came into this last book with sort of a ho-hum attitude. Honestly, I could have taken it or left it. I'm not the biggest fan of historical/steam punk novels, so although I felt like the characters were intriguing, I was a bit put off by the era and language. Not that it's bad, it's just not my thing, really. But, unless a series is really BAAAAAAAAAAAAD I usually continue on. So I did, and I'm glad I did. 
 I'm happy with the direction Cassandra Clare took this story--up until the epilogue, which I'll get into in a moment. Ms. Clare has a definite talent for creating well-rounded, believable, sympathetic characters--especially her boys. Don't get me wrong, I like her girls just fine, but she just knows exactly how to write boys that I will swoon over. Her Jace from TMI is my #1 absolute favorite character--boy or girl--and I really liked Jem and Will as well. 
 One of my favorite lines from Clockwork Princess: "You know my music." ~ Jem. Big, Fat. Swoon. 
 And then: "You are as dear to me as the other half of my soul, Jem." ~Will. *dead* 
 And let's not forget: "We are more than brothers, Will." ~Jem. *jdgfkjgafkedkyg* 
 So, apparently, I ship Will and Jem over all else. Though, it isn't like they didn't deliver the swoons with Tessa either. They did. 
 "I love you so much, so incredibly much," he went on, "and when you're this close to me, I forget who you are. I forget you're Jem's. I'd have to be the worst sort of person to think what I'm thinking right now. But I am thinking it." ~Will. *gah!* 
 I mean, can you even stand it? I can't. 
 All right, swoons and all aside, there was a lot to like about this book: side characters, the romances, the place settings, the pretty clothes, etc., etc. But there were also things that stopped me up. 
 1. Description. The description in this book (this whole series) is way, WAY overdone. Everything is described down to the smallest detail. While that is great for bringing the picture to mind, it also bogs the narrative down and makes the reader impatient. I will admit, I skipped some of the scenery description in favor for some dialogue or even internal thought. 
 2. Climax. Honestly, it felt . . . like a bit of an anti-climax. It was over much too quickly, much too easily. I don't know. It just didn't feel like such a big deal in the end. 
 3. Epilogue. (view spoiler)[ Now, I know this is just a personal preference, so I don't really want people arguing with me over my opinion, but . . . I didn't really like the epilogue. I would have preferred the story to end right after the last chapter. I'm not a huge fan of epilogues to begin with, but for me, this one was a case of "too much information." I don't like reading about character deaths. I just don't. I like to continue to imagine them together, having adventures, and being happy and in love forever. It was bad enough knowing that Tessa was immortal, and that no matter who she picked, she would outlive him. But I did not enjoy, nor want to read, about Will dying. Yes, he had a good, long, happy life with Tessa. That's wonderful. I just don't want to read about it ending. I don't like it. 
 Then there's Jem. I love Jem, I really do. But I am a one man, one woman forever kind of girl. It doesn't sit right with me that Tessa kind of sort of chose Will (by default, really), then he dies, and now 100+ years later when Jem finds a cure and is released from the Brotherhood, she gets him too. I'm sorry, but it just didn't sit right with me. I wanted her to love Will and only Will. I wanted her to CHOOSE. Yes, she lives forever. I don't care. I want her to love JUST Will! Sigh. Alas, that's not the way it was written, so I guess I'll have to live with it. I wasn't UNhappy, I was just . . . conflicted. Disappointed. (hide spoiler)] 
 One other thing I did really enjoy was the family tree! Yay! We finally get to know for sure who came from where, and how Jace and Will are related. So fun! 
 All in all, I think ID fans will like this ending. I may have had my issues with some things, but I did enjoy the read. I would recommend it to friends.