I have to agree with everyone else that this series has potential. The art is great--the characters and the backgrounds all have a distinctive style that's somewhere in-between modern and fantasy. The premise is tried-and-true: a super powered delinquent must learn to control his powers and get along with his (also super powered) classmates. And the lead character is solid; he's powerful, but not arrogant or annoying. So yes, the series has potential. But at some point, a manga has to grow into its potential, and for me, it's long past the point where this manga should have done so.
The problem with this series is that while the main character is good, the other characters are poorly developed and the plot is largely uninteresting.
As far as the characters go, the mangaka doesn't make very good use of them. For the most part, the majority of the characters feel like they're there just to be there. For example, in the latest chapters, the cast has traveled to the home of one of Rin's classmates because there's trouble at his family's temple. We're given to understand he has some anger toward his father (the leader of the temple), but that's the extent of his character development. While the temple leader plays a major role in the events, the classmate strangely does not play an important part in the storyline; in fact, his part ends up being no bigger than usual.
Even major side characters like the female lead and the main character's twin are disappointing. Despite sharing a close relationship, the twins don’t get much opportunity to work together, and when they do interact, Yukio acts more like Rin’s teacher than his brother. The female lead is also under-utilized. She's intended to be cute and "inspirational," but I find her unlikeable and unsympathetic. Despite being quite powerful, she is convinced that she's a weakling, and thus spends large amounts of time wallowing in self-pity and berating herself for her supposed weaknesses. (What part of this does the mangaka think we will find cute or inspirational?) Even worse is the fact that there is something of a love triangle between her and the two brothers.
As far as the plot goes, this to me is the greatest weakness of the manga. With all the shadowy conspiracies and exorcists and devils running around, you’d think this would be a really, really exciting story, wouldn’t you? It’s not actually. There’s no real focus to the plot, villains appear out of nowhere, events happen seemingly at random, and it’s impossible to tell what the story is building towards at any given moment. There doesn't seem to be any point to the enemies the characters have fought, or to any of the storylines (especially the long "Impure King" saga) except to provide Rin with a chance to level up. Nothing that's happened so far has any direct connection to the defeat of Satan, which is supposedly the larger goal of the series. It feels more like they're fighting bad guys because that's what you do in a shounen manga, not because fighting these particular bad guys is advancing the story in any way.
And worst of all, I find the chapters increasingly boring. Rather than developing the major characters, the mangaka seems to prefer wasting pages on needless details like the shadowy back history of a character or a religious sect that will probably never appear in the manga again. (Just how much did we really need to know about the inner workings of Myou Dha?!) If I don't see the point to the plot and I haven't been made to care about any of the characters, then the manga isn't one I can continue with. For now, I’m putting this series on hold.