Among all slow started shounen D Gray man beats them all. It takes a good 40-50 episodes before it really kicks of. It starts good enough but theres a huge gap with fillers snd more episodic adventure stuff in there. But once you get past thatit does get really good. So patience. Of if you like skip fillers. But one should definetly give it a chance until it picks up. At that point plot gets interesting. The background of characters. Good fights. The darker artstyle. Music is good.
Unfortunely it kinda ends with cliffhanger and the follow up is not as good. Hopefully they will complete the anime story someday. If not ill read the manga but really whats here, especially from around episode 40-50 and onwards is great and was worth the wait.
