Do you think that Attack on Titan is good enough to maintain any kind of legacy? Will people still watch it in 20 years?
Sure. I might have my problems with the series (like the pacing, characters dying before they can properly develop, etc.), but I do think that it has enough staying power to remain popular. Though to the show's disadvantage, it doesn't have the rewatch value of something like Cowboy Bebop or FMA. But that's just my opinion.