While I devoured the first two books in the Infernal Devices, Clockwork Princess took me forever to read. I'm still not sure why, but maybe I was losing interest in the Infernal Devices world and was paying more attention to the current world, The Mortal Instruments. Who knows. What ever happened, Clockwork Princess frustrated me more than anything. Tessa is one of those girls who can't choose between her guys, Will's tortured soul was bugging the crap out of me, and Jem - well, I think he was the only character I started to feel for until the end, when Clare decided that something wasn't going to happen. I'd rather that thing happen instead. To me, it felt like she used a cop-out ending for Jem's existence.
What I did like is that we finally figured out what Tessa's Clockwork Angel was, and who she comes from. I also liked that bond between Will and Jem, which seemed to be stronger in this book than the other two. There are also some other characters that become stronger players, such as Will's sister and Sophia, the maid of the Institute. Also there is more to the automan's than we saw in the first two books.
The other thing that bugged me is the dialogue at the ending. The conversations that centered around Jem seemed to over-emphasis a certain fact, and it got irritating after awhile. I won't say what it was so to not spoil it for those who haven't still read the last book, but it is a point that should probably only be emphasized in at least one or two conversations, not from a million different point of views.
Now that I finished the last book of this trilogy, I'm impatiently waiting for the next book in the Mortal Instruments series. If I had to choose, Mortal Instruments is probably more of my choosing. It's nice to know the origins of that world, but Infernal Devices does not necessarily need to be read before hand.