>TBH I never understood the hype for this show.
Your question is too vague but I'll try to answer it.
•The characters have fun, interesting and cool personalities with enough complexity to keep the audience engage.
•The setting and power system are detailed and unique enough for it to stand out from the crowd.
•The series is long enough convey it story properly and doesn't overstay it's welcome.
•The plot doesn't trip over itself and goes to shit.
•It's dark but still hopeful.
•It's "anime" but not too "anime" for a general audience making it great for beginners.
There are more reasons but I made my point.It's a very well rounded series which can be enjoyed by a wide audience.