@Klordz For the type of artystyle I think it's done fairly decently. What matters isn't really how bad he looks but the reactions of people who see it.
Unless this was more of a gore/horror type of thing and or done with a different art style. I don't think it's too necessary to worry about how well done the acid burn looks.
It's fine. Too much detail would take too much time drawing and redrawing it.