You can tell several things by reading Clockwork Angel after the first three Mortal Instruments books: Clare gets better with every book she writes, she truly enjoys the Shadowhunter world, and she only knows how to write certain types of characters. Will Herondale is almost a carbon copy of Jace, albeit slightly more unlikable. Jem is Simon, Jessamine is Isabel, Tessa is Clary (though much, much less annoying and more talented), the villain (who I won't reveal due to spoilers) is Valentine... you get the idea. It's basically a copy-paste of her first trilogy, but she's toned down or ramped up their personalities only slightly to make it different enough. If you can get past that, it's actually a rather enjoyable story. Tessa is a highly capable shape-shifter living in Victorian London, who runs into the shadow hunters and learns all about the world she didn't know existed or was a part of. The Clockwork creatures provided a nice touch, and added an interesting mystery element to the story. The double reveal at the end was well done- and I suppose easy to spot if you knew what to look for, but I was happy with it.
One of the only sticking points I have here is the character of Will Herondale. He was so smug, nasty and narcissistic, that I had zero interest in him. Yes, I understand he's got some tragic backstory that lead him to act that way, but so did Jem, and he's not an ass. The very fact that Tessa was drawn to him was infuriating. I have a feeling that Tessa will end up with him- so he'd better do a complete 180 if Clare wants me to hop on this ship. My favorite character was Henry. Let's see more of him in the next one, huh?
I will definitely continue with this trilogy, but not right away. I need a break from smarmy Will.