Muhyo to Rouji no Mahouritsu Soudan Jimusho is one of the (many) series I hold up as an example of why it's never a good idea to depend on rankings, comments or recommendations when picking out manga to read. Despite its so-so ratings, the lack of gushing comments, and the unimpressive number of people who're even aware that it exists, this is one of the better shounen supernatural titles out there, superior to plenty of higher-rated manga in the same genre.
Plot: Not what I'd term "brilliant," as there are no mind-boggling twists and the endpoint is fairly straightforward, but very satisfactory in the sense that Nishi Yoshiyuki has a clear idea of where he wants to go with the story and guides it unerringly in that direction. Not once does he introduce unnecessary spin-offs in an attempt to milk the cash cow -- which, for a Shounen Jump series, is one of the highest compliments I can give. The first three-and-a-half volumes follow an episodic format so as to introduce the reader to the world and the characters, but from the middle of the fourth volume onwards it takes off at a steady and apt pace until the main plot is over and done with.
World building: The refreshingly original concept of Magic Law in place of more typical methods of exorcism set the series firmly apart from others of its ilk. It's very creative and plenty of fun.
Characters: In the end, one of the things I loved the most about Muhyo to Rouji. Most of the significant characters have distinct personalities that don't conform to the usual shounen tropes, and each had a clear role to play in the plot; never did I find myself thinking "this character needn't have existed." The interpersonal relationships were also lovely: they're friends, family and a team. They help out with one another's work, provide emotional support when someone's down...and give each other a good talking-to when need be.
Action: In a welcome deviation from the standard shounen fight formula, all significant battles require equal amounts of strategy, skill and strength. So despite Muhyo's incredible talent and Rouji's vast reserves of power, other characters never felt superfluous: everyone pitched in with their own talents to help achieve victory.
Humour: The mangaka never aims for big laughs: instead, every volume has numerous instances of situational comedy worked in here and there -- and it worked like a charm to lighten the heavy atmosphere, especially later on. The character profiles, letters to the mangaka and Q&A sessions with the characters were inspired additions.
Ending: The only part of the series I didn't like, and the reason I can't give a higher rating. The penultimate volume dropped heavy hints that there would be a last, strongest opponent to come, but the finale didn't follow through on it at all. I think it'd have been better if those hints had been scrapped, because the rest of the story stood perfectly well on its own. As it is, Muhyo to Rouji ended with a huge "Will the future hold even more horrors?" hanging over the characters' - and the readers' - heads, which leaves you with an unnecessary sense of dread in the midst of an otherwise happy ending.
Conclusion: A very enjoyable ride. Recommended whether or not you're a fan of action shounen, as long as you enjoy the supernatural genre and don't expect a "super mature" (a la sex and heavy tragedy) reading experience.