Pretty random thought, I have that in mind for a long time and reading a post somewhere else in the forum made me think of something else that I connected to this idea that I now want to post.
The reason why I like mangas so much and I got bored of european comics is linked to anthropology theories that explain that every society's goal is to produce symbolism. I feel myself attached to the production of symbols (art, etc.) and the understanding of their meaning. I am fond of myths especially underlying/founder myths. I think it helps me to understand the real world with abstract objects.
I also find this symbolism in manga characters, but the european comics seem only constructed around a scenario and a universe. It makes me feel the characters could be interchangeable, the story would be same, while the manga characters carry a real value through long adventures.
The personality of a manga character could be exaggerated, not in the norm or considered as unrealistic, I don't mind, since his or her symbolism can still bring me something to understand.
Actually, in terms of meaning it is not necessary supposed to be complicated and I also like reading manga where the symbolism of a character is simple and obvious, as long as it is not caricatural. That's why I like so much the character Naruto. I am envious of children that grow up with Naruto and the positive message that this manga brings to them. Myself, I grew up with Dragon Ball (anime). That was cool when I was young, but it is kind of void and now that I am a grown-up there is nothing left that interests me in DB. If I had Naruto back then, I would have been a good person now

and I predict a bright future for these kids

I am also indulgent with "out-of-character" behaviors, sometimes the author wants to tell something, but gets lost and makes the things awkward and kind of unbelievable. It can be difficult to pass a message.
On a side note, I am not very fond of mangas that want to depict the reality. The mangakas don't really explore what their characters are supposed to represent and concentrate on situations supposed to be real life. Somehow, I know the reality too well to receive any interesting message from this kinds of manga. I gave up Solanin for example after a few chapters, it was hard to follow guys that kind of abandon their efforts to reach a better a situation (perhaps it is different later, but I could not continue).