D. Gray Man
6/10 ONLY because of the ending.
The reason I said 6/10 was because near the end they raise up lots of questions in your mind, and leave you up there, in your mind you're saying "OMG I can't wait until I figure out who is the 14th Noah, OMG When will the Earl die? Will it ever stop?
They don't ever answer those questions, they might have kinda answered the 14th noah but many other questions are open ended.
But, the storyline is awesome 10/10 for that. :D
I REALLY recommend watching this series, But near the end, Prepare to not get your most struggling questions answered. But since its open ended, there might be another series, Or you can just make up your own.
Again, HIGHLY reccommended.