Mikasa has extra costumes that can be unlocked through completing the main campaign or completing requests in the home base. While they do not affect your stats, the costumes do make you look ...
The truth is, AOT came out at a time when 90% of anime were effortless softporn and moe; so it stood out. If it was made along with Death Note or Code Geass, it would only get a fraction of its hype.