Hah, if realism is the only thing that describes Ikegami's art, he wouldn't be considered above mediocre American comic artists. Expression is what makes him a superb artist.
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His characters are incredibly charismatic.
But the important thing is his art suits the story he works with. What Koike wrote for Ikegami's, Nagai Go's, Adachi's, Kojima's art, etc. are massively different from each other. That's why Koike is a master writer.
Mizayaki's style suited the story of Nausicaa the best, because it looked like illustrations from some fantasy literature books. As Lone Wolf and Cub's art looked close to Japanese traditional illustration of a samurai tale. I can't imagine it in a different style.
Authors like Osamu Tezuka, Hayao Miyazaki, Kazuo Koike, Buronson, Go Nagai, etc. have lived through the harshest time of Japan, the post WWII period, that is why their works are so painstakingly sweeping and soul-touching. For Tezuka it was the theme of rebirth of Japan, for Miyazaki it was the Post war democracy which later led to the collapse of his Marxist ideal, for Koike it was the time where authors fiercely protested against the government and their own society. Same for Alan Moore who lived through the cold war, which gave Watchmen so real a tension and horror of that period.
What does a snotty-nosed kid who grew up in comfort and had parents who let him draw all day like Eiiji know about pain and suffering? He doesn't even know love. To try to compete with classic manga in those fields is foolish. But again, this is a shonen series. And Eiiji is quite a fun character on that account.