This series is amazing! To each their own, I grant you, but there's a reason why a kind somebody held on and translated through volume seven. If you don't like mystery novels, don't read this. But boring? NO! Challenging, yes, but not boring in the slightest if you like the genres involved!
To me, this series is not only readable, but enjoyably and rewardingly RE-readable. The plot structures are ambitious, true, and that ambition increases with every novel or so, but the author has an experienced touch and mostly keeps it on track. Well, except when he blows that track apart! (I'm looking at you, gambling island arc!!!) The characters have a nice balance of richness and recognizability, necessary in an ensemble cast.
The level of creativity is astounding and, as a former writer, I can tell you it blows me away how he keeps coming up with even more creative twists with each volume. How can he make it look that easy?!? You can see the author has fun with the Package concept, of which saying much more would become a spoiler. But it creates a mystery novel/spell folklore cross of a trope that has some of the most enjoyable blending of disparate elements that I've seen in a while.
I would put this series up there with the reality-bending English-language graphic novel Ronin, which I bought one summer and suddenly found that fall that we were studying extensively it at my ivy-league American university. This series is not quite the same mind-...uh, -twist, and of course it is not as concise the one-volume comic was, but the further you go in, the more impressive it gets.
I would turn the rating up to 11 if I could.