Most of the problems I had with this book can probably be laid at the feet of the translator and whoever was supposed to edit it once the translator was done with hit. Like a lot of people have already said, the sentence structure and punctuation leave quite a lot to be desired. The publisher seems to have not bothered with an editor beyond the translator.
I do think the story could have been about 50 pages shorter. A good half of the book involves little vignettes showing us what each former member of the Blades is doing, and it isn't until about page 100 the bunch of them finally get together and start working on the job they've been assigned.
I did like a lot of the dialogue. The characters often engaged in the sort of give and take you would expect in a rollicking adventure story. That aspect of the story was fun.
Athos make a guest appearance, which I liked, as it fleshed out the world and placed the Blades within the same context of The Three Musketeers. The cardinal, while a political animal, wasn't nearly the rat bastard he is usually portrayed as.
I don't know that I'd read any additional books in the series (the ending definitely indicates a continuing story), but I don't feel like I completely wasted my life in reading the book.