I'll start with the plot, which is far darker than your average shounen. From the very first episode, we are shown a merciless enemy that will exploit any weakness, who's main weapon, the Akuma (demons) uses the souls of the dead. These are not zombies, just mindless corpses. These are weapons which pull a soul back from heaven and torture it as their power source. A lot of shounens gloss over the concept of death, bad guys are captured alive or shown the error of their ways, people fall unconscious but can be healed, etc. In D. Gray-man, death is very real, and resting in peace is only for the fortunate ones who's loved ones are strong enough not to be tempted to call them back.
Against the Akuma and their creator, the Millennium Earl, are the Exorcists of the Dark Order. Exorcists are those chosen by God to use 'innocence', a mysterious substance which can be used to form weapons capable of destroying the Akuma. The series follows Allen Walker, a new recruit with the ability to see the souls trapped within the Akuma. The plot itself begins slowly, with short arcs in which Allen and his comrades are dispatched to investigate mysterious phenomena which are thought to be caused by innocence fragments. After a few of these arcs, the Noah Clan, allies of the Millennium Earl, begin to be introduced and the focus turns to the war between him and the Dark Order.
The plot is, for the most part, very well paced. Early arcs are kept short, about 4 episodes or so long, with a single 'filler' episode in between. Don't be put off when I say filler. While the plot could easily go without these episodes, I found them all to be entertaining (if somewhat silly at times) and they served well as comic relief within an otherwise serious plot. And if you don't enjoy them, they do become fewer and further between as the war intensifies and plot arcs become longer. With one exception, none of these longer plot arcs drag on to the point that the viewer just wants them to get on with it. In the one arc in which this does occur, it is saved in part by having another plot running at the same time. Battles often do last across multiple episodes, but in most of these, the battle changes and develops over those episodes, unlike drawn out battles in other shounen which just get repetitive, where the middle episodes can often just be skipped entirely.
The show also boasts one of the best sets of characters of any anime I have seen. Each hero is flawed, and the Earl and Noah are far more fleshed out (in more ways than one in the Earl's case) than most villains. It says a lot about the quality of a series' characters when the villains mourning a dead friend can evoke sympathy. They also managed to inspire doubt as to whether the exorcists are in fact the good guys, thanks to the show's religious imagery.
As for the heroes, each has their own motive, each of which is more complex than the standard shounen motives of just saving the world or becoming the strongest and the like. Allen wants to save the souls of the Akuma, to the point where he can even show disregard for his own or others' lives at times. Lenalee, the series' main female character, fights for the sake of her friends and brother, and her past reveals that she may not support the Dark Order's cause even as she fights for them.
My personal favourite characters were Lavi and Bookman. These two are a master (Bookman) and apprentice (Lavi) of a clan of historians who became exorcists to be close to history as it occurred so that it could be recorded, and while they do fight, they try to minimise how much they interfere. Lavi's conflict between his duty as a Bookman and as an Exorcist, the loyalty he developed for his friends despite Bookman's orders to become close to no one, and his doubts as to whether the cheerful, friendly, fun guy is the real him or a mask that he should remove was probably my favourite aspect of the series.
So, here I am singing the series' praises, yet it got a 9, not a 10. Why? Well, in complete contrast to what I said at the beginning, because it ended. A lot wasn't able to be explained before the series was cancelled. The last ten episodes or so suffered from trying to rush one of the story arcs after having taken their time over previous ones. The battle in the last three episodes was amazing, but it also wasn't the final battle that I wanted to see. There is a lot of potential for a sequel, including a development at the end that virtually screamed "to be continued". I do sincerely hope that there will be a sequel. But if there isn't, the show ended in the best possible place it could. A clear cut ending is often unrealistic, and endings in which the heroes won but the villain is there in the shadows, not as dead as they thought, muttering "This isn't over" gets old quickly. Maybe the abiguity was for the best.
All in all, the show is well worth watching, even if you don't usually commit to long running shounen. Just don't go in expecting to not have any questions at the end.
