My opinion of Sanderson is declining. This book wasn't as good as the first one, and that one was a step down from "Alcatraz vs evil librarians".
I am fine with the setup and the characters(except Elend). I didn't like the pace, and I didn't like the anti-climactic way Zane was dealt with.
The denouement with the spy was altogether predictable - makes you wonder why there wasn't an allomantic metal to sharpen the brains.
Straff Venture was overblown, the Koloss had convenient features all at the right moments for only the protagonists to take advantage of.
Elend's final state was shoehorned in. It doesn't fit the tone of the story.
Overall you could read just the beginning two or three chapters and the final two or three and you'd be no worse off.
My rating is a 3.5