I recently finished Kraken. It left me unmoved. But I would really love to hear someone else's opinions.
Ok, well - I decided I just won't find the time for a proper review, but here are a few thoughts:
It's quite entertaining, but no more than that. It's definitely not Mieville's strongest book. It follows a pretty standard formula of a hapless individual suddenly sucked into events beyond his understanding, and discovered that the world is a lot weirder than he thought.
The problem is that the actual events that happen, while individually cool, seem to be mostly a random series of events. There is an overall plot, but it boils down to "there are a lot of different groups fighting, and it's not clear who is good and who is bad", which gives an excuse for a lot of chaos. And there is a whole sequence where every chapter or two involves the introduction of a new enemy that is The Baddest Thing Ever, only for said enemy to be easily dispatched when it's time for the next Even Badder threat to show up.
Also, there is a whole lot of lip service paid to the fact that this takes place in London, but to be honest, I didn't feel like any of the events had anything to do with London itself at all. Sure, there's a group of Londonmancers, but they could just have easily been called Praguemancers or New-Yorkmancers. This story could have happened at any large city.
I guess this tendency for chaotic overcrowded plots is a feature of much of Mieville's writing (The City & The City being a notable exception), but normally the plot itself is more original and exciting. Here, it's a relatively run-of-the-mill "a secret magic underworld hidden in the real world" story, and while it can be very entertaining, it doesn't have that much to say.