Probably because, even though there are creatures "that do not exist in the real world" the characters are very real. They can pass any kind of feeling they feel for the person who's reading / watching. They behave in a way that any human being would behave in this situation. So I say, what wins the audience, are the characters. What good have a perfect and unique history, without even developing the characters? Then a point to Hajime Isayama for creating incredible characters.
And well, that magnificent history. A whole new world, scary and unlike anything we were accustomed. This was a blow to me! But at the same time, very good. For a long time I did not watch anything that really let me weeks, months thinking about what might happen. From the first chapter / episode SNK this being one amazing experience for me. Thank you for creating this perfect work Hajime Isayama. Well, here it is basically a summary rather small compared to my opnion complete, but that's okay, because if not it will be very big here XD
