In short: Clockwork Prince by Cassandra Clare is an exciting sequel featuring heart-wrenching story developments that make for a truly addictive read. 
 Cassandra Clare has a true talent for messing with her characters' emotions, putting them through hell just when you think they might get a happy ending. This in turn causes the reader to be put through hell too as she also does such a good job at making us fall in love with her characters that it is all the more heart-wrenching when terrible things happen to them. Heart-wrenching sums up my feelings for Clockwork Prince pretty well. And I loved every second of it. 
 I know I say this in every review of Cassandra Clare's books that I write, but I am terribly fond of her characters. Somehow, Cassie has managed to come up with a whole slew of enigmatic characters just waiting for us to read about to uncover their secrets and mysteries. Every character, main and side, have their own unique and well defined personalities and their own intriguing back stories. It's addictive, this need to uncover the new additions to the seemingly endless backstory reveals for each character. From the moment I opened Clockwork Prince, it was a race to the finish. 
 The plot progresses nicely in this sequel. Not only are characters changing and developing (in Will's case, drastically), but the plot line surrounding The Magister, his clockwork creatures, and the mystery behind what sort of magical being is Tessa, continues in a rather intriguing way, with lots of action and surprises. It still came off as the second book in a trilogy in that there was a definite building up of even greater things to come, but at no point did the plot seem like unimportant filler as is often the case in second books. 
 My one quibble is the introduction of the love triangle. I find that they mess with my mind too much, and not in a good way. I find them a bit stressful, to be honest. I would have preferred to have seen more action scenes in the stead of all the love triangle drama that crowded the end of Clockwork Prince. Despite this, Clockwork Prince was an exciting and addictive sequel to an amazing series. I would highly recommend giving The Infernal Devices Series a try if you haven't yet, and checking out Clockwork Prince when it's released December 6, 2011!