i agree, the facial expressions of onizuka in the anime is priceless. this is actually a major reason why i watched it
if i remember correctly, onichi at the live-action series didn't use it much. but it was more during the drama special and the movie, which looks stupid. however, the live-action series did have a better story, especially the ending IMO, than the anime.
the movie sucks though
and the drama special was just ok... nice of them to base the lead character to kanzaki