I've been reading this series since it came out - every couple of months anxiously checking to see if the next one is done. Considering how many books and series I read, the fact that this is the first one I check for whenever I log into Amazon says a lot about how much I'm enjoying it. From the first book, the interesting and original ideas flow and the worldbuilding is second to none. That by itself would make the series worth reading, but I also very much enjoy how logical and realistically the characters are written and how they use their brains to solve problems. To be fair, smart characters are a hallmark in general of this author, but I can tell that all the books he's written have really added to his skill and this series is the culmination of many years of effort at writing and Mr. Blood is at the top of his game.
Speaking of intelligent characters, another reason I love this series is because I never really know what is coming next. Every book has a surprise I just didn't see coming. It's difficult to surprise me as I'm so familiar with all the tropes of fantasy and sci-fi, but somehow this series manages. Honestly, it's a big part of why I look forward to every book.
There are some editing errors here and there, but when it comes to solid worldbuilding, intelligent, thoughtful, and logical characters, as well as deep mysteries and surprising events, this is a series you won't want to miss.