That was surprisingly bad... for this viewer, anyway. It's newbie-unfriendly. That's a very different thing, but the distinction is subtle if you're a newbie. D.Gray-man is a long-running shounen manga (2004 onwards with interruptions for health problems, 25 volumes) that used to have a long-running anime (2006-2008, 103 episodes). The manga creator had a few objections to the latter and got involved more personally with this 2016 anime, but it still didn't work for me.
If I'd watched or read all of the original D.Gray-man, though, I'm sure it would have been great. I can tell that the story's strong. However that's only in theory if I can't tell the difference between most of the characters and I don't know what their relationships are based on.
You see, they don't re-establish the characters. I didn't know who was who. I could tell that Allen Walker was the protagonist, but beyond that I was lost in a soup of interchangeable exorcists who fight monsters and have no sense of humour. The men are boring. (That's most of the cast.) The women are rarely glimpsed. (Even Lenalee Lee just came across as someone who cared about Allen Walker for reasons unspecified and clearly had some backstory that might well have been quite interesting had I ever been told about it.) The show's first half I found soporific, but then found myself getting increasingly interested in the second half as I got a firmer grip on who these people were.
I should probably tell you the show's premise, by the way. Exorcists are at war with Akuma, who want to destroy humanity. This has been going on for millennia and is all very Biblical, with the Pope, the Noah family, the ark, apostles, churches, priests, etc. However it's not entirely clear that the exorcists are that much better than their enemies, with sinister secrets and some deeply suspicious people on the payroll. There will be quite a lot of fighting (which is time-wasting), but also some juicier, nastier plot developments and the bloody deaths of important cast members.
My journey through the show went as follows:
EPISODE 1: empty shounen fight scenes. However those are followed by a cool plot development in which our kind, good-hearted hero Allen Walker learns that he's sharing his soul with some kind of apocalypse monster, called the Fourteenth. It's going to take over his body and mind. Allen's personality will be erased forever and he'll have become one of this universe's ultimate evils.
There are also flashbacks to a clown. I'm pretty sure these are supposed to be important and meaningful.
EPISODE 2-3: a monster-of-the-week story with a body-jumping phantom thief. It's quite good, though, and it introduces someone who joins the heroes to become another Exorcist... but he then never appears again. Am I wrong?
IT CONTINUES: silly Akuma attack indistinguishable heroes, some of whom have been doing some really nasty things to avoid losing the war. You may or may not care which side wins. Someone's been in a coma for nine years. Someone used to be Someone's friend when they were children and we see Someone and Someone in yet more childhood flashbacks when Someone sends Someone, Someone, Someone and Allen Walker back into those early memories. (These people do have names, but that's how it played to me.) There are hallucinations and there have been cycles of dying and regenerating.
AND STILL IT CONTINUES: that's a bit brutal. Missing limbs and stumps. I'm still mostly bored, though, despite the evil ideas (e.g. half-Akuma).
NEARING THE END NOW: in fairness, the Kanda/Alma stuff would have probably been good if I'd been invested in the characters. Even as it was, I eventually came around to finding it watchable. More fights (sigh), but these ones are more likely to have strong emotion underneath.
THE LAST FEW EPISODES: are actually good, even for a newbie like me. The story's got going properly now. Allen's situation is great. The Order's misunderstandings are potentially catastrophic but understandable, while the baddie will kill anyone who crosses their path, even from the show's core characters. I quite enjoyed all this... but I was still left wishing I'd known more about Lenalee, Kanda, etc. Similarly, what's Allen's backstory with that bloke he calls "Master"? His story involvement would have had more weight if to me he hadn't just been another Someone.
...but then it doesn't have an ending. It just stops. Are they planning another season?
If you know D.Gray-hollow, watch this show. I'm sure you'll like it. It feels big. The darkness, tragedy and morally questionable actions are rich. I'm sure there's a lot going on thematically, although I'm not sure that the Biblical elements would necessarily hold up to knowledgeable scrutiny. (Anime tends to regard Christianity as a source of mythology and doesn't tend to care about any of the details.) Personally, though, I found that most of it left me cold. The show wasn't catering for me at all and all the fight scenes weren't encouraging me to try to overcome that either. This is a grossly unfair review since I'm basically whinging that most of the show went over my head, but if you're not already a D.Gray-man fan then I'd expect it to go over your head too.