Yuukoku no Moriarty is an unconventional re-imagining of the classic story, with Sherlock's arch-nemesis as the protagonist. For better or worse, the author didn't have the courage to go all out and keep him a self-serving master of crime. In this version, Moriarty is an underdog who goes from rags to riches, and grows up to become a merciless vigilante on a crusade against corrupt nobles.
Incredibly cheesy, right? Yes, of course, but not without potential for some nice, juicy moral ambiguity. Does the story deliver on that front? Well... yes and no. Kinda.
You see, Yuukoku no Moriarty can be split into two distinct parts:
the fun one, and the NOT fun one. The manga is at its best when it focuses on Moriarty vs Sherlock mind games, and at its absolute worst when it focuses on our protagonist fighting evil nobles. And they are eeeeeevil, all right. Evil with a capital E. But, first things first, lets start with the good part.
Moriarty and Holmes are both compelling characters. One is a ruthless and brilliant killer, but driven largely by compassion for the oppressed. The other is a likable and eccentric genius detective, who sees solving crimes as the best source of entertainment. The two are good foils for each other, and their antagonistic relationship is the manga's strongest point, even at this early stage.
Other reocurring characters can also be interesting; from Moriarty's cold hearted brother who idolizes him, to Sherlock's upright buddy Watson, we have a decent variety of personalities.
So... let's get to the “not fun” part now, shall we?
The chapters that don't deal with Moriarty vs Holmes, have monster-of-the-week structure. It usually goes like this:
1. William (Moriarty) learns about some acts of cartoonish villainy committed by an evil noble.
2. He investigates.
3. He and his sidekicks easily kill the evil noble.
4. Rinse, repeat.
Those minor antagonists have exactly three roles to play in the story: being cruel to commoners, gloating evilly, and getting their asses handed to them by our anti-hero. They're completely one-dimensional, they're pathetically weak, and they NEVER pose any threat to the protagonist. They usually don't even put up a fight before he finishes them off!
As a result, the chapters that focus on them have no dramatic tension and no thrill whatsoever. They're about as boring and cartoonish as it gets, and they're the vast majority.
When you read Yuukoku no Moriarty, you can tell at once if the chapter will be entertaining or not by checking if Sherlock graces it with his presence. If he doesn't, you're in for a snore-fest of the worst kind.
Keep in mind that this is a rather new manga and only 16 chapters are available for the moment, so there's probably a lot of time left to iron out the kinks. So far, I think that the good bits make it worth putting up with the bad ones (if only barely). I especially recommend it to fans of Death Note and Code Geass, but only as a poor man's substitute.