Given the success of this work, it's easy to see how Bisco Hatori came to fame. Or, at least, fame as far as you could call a comic artist.
As the longest-running series by Hatori-sensei, it bears a very large change between the beginning and end of the story. As she took time off of Millennium Snow to work on this series, it become immediately apparent why that might have been: this story just has so much potential!
Although played as comedy, there are still many heartwarming moments throughout the early chapters. Having an extremely 90s art style while playing up the eccentricity of the characters certainly helps drive home the humor, and it's no secret that this is Hatori-sensei's strong suit.
By the end of the story, however, things have changed dramatically--drama, in fact, is the largest of these. The story begins to include many plots wherein the characters may fight or cause on another trouble in some way. Although not tragic characters by and large, they still manage to come through as genuine because of the effort they put into everything they do. Although never played up for depression points, each characters has a history.
The art evolves into a modern style by the end, showing off a much rounder look; specifically, more realistic in appearance. It looks very clean and suits the more dramatic elements of the latter half. As drama and romance are played up, the art moves away from the "glitter and glitz" screentones and overly-dramatic pictures to more subdued and soft effects.
Overall, the story is definitely worth reading no matter what types of story you like to read; don't be fooled by the romance and comedy labels, as these are certainly not the extent of everything Ouran High-School Host Club has to offer.