First of all, the efforts on the underground comics were not heavy. The drawing style was the obvious differences that the artist used simple line works less details. With the simple story, i think it suit to the simple line works. And with the simple storytelling, characters became more relatable unlike the hero or a person who like to travel around.
What I enjoyed the most was that since it was the 'underground' comic, which mean that less regulation. Im pretty sure that the artist who worked on underground comics had more freedom to express themselves and the character unlike the mainstream comics, since it was targeting as many people possible. It might be one of the advance underground comic artist would enjoy about. Sometimes the 'nice' words do not work at time at the certain circumstances.
but it could not avoid the fact that some authors overused their freedom. I do not know it accused the issue at that time too, but now their some sexual/ racism approaches might brought argument.