The animation and music are both awesome.
It has a decent plot. Not great, but it's more than most people give it credit for.
It has likeable characters, and it evokes a real sense of danger and suspense, which keeps you on your toes and keeps it interesting. The fights are good.
These are its strengths imo.
But, as with many things nowadays, if people see something and didn't really like it, and then see other people really enjoying it, it's "overrated." If you want a sense of its quality, you should watch it for yourself. I highly recommend trying it out, but don't let what people say here determine its quality for you.
