There were three books between that trilogy and this newest one. The first, called Best Served Cold, is in the process of being turned into a motion picture, and will likely be most people's first entry into this fantasy world. The third, called Red Country, is probably my favorite of all of his books as it returns to an interesting character from the original trilogy while putting a Wild West spin on the story. The second, called The Heroes, is an interesting take on the genre as it is written entirely around a single battle, but it is my least favorite of all of the books that I have read from Abercrombie thus far.
I mentioned the second book last because The Age of Madness trilogy dragged for me like that book did. As a whole, I find it a well-constructed story with some remarkable (but believable) twists in both plot and character development. By the end, I was riveted, but it took a while to get there. The first two books took me months to read, but I read the final one in under a week (granted, this past weekend's power outage had something to do with that). It was definitely worth it to get to the end as the entirely trilogies big reveal made me rethink the entire trilogy.
I would, however, like to now read a series with heroes who are a little less ... flawed.