Well, is one of my favourites, but not the best.
I can try to explain why i think it's "so good":
- the psychological themes used are great (kinda disturbing for some people, but great).
- the religion references are vast and give the series a different "flavor".
- the action is short, but great.
Some people i know don't like it, not because it's "boring", but because is very complex, "weird" and hard to follow. They are right, but i think of that as a good thing, not bad.
I watched the series 4 times, when i was 9, 12, 18 and 21 years old. I only got the meaning of it ("my" meaning at least) the last time i saw it (maybe because it was the only time i didn't see it with portuguese dubs or subs ^_^).