As a character actor he is really skilled. he can look really fancy or really plain or even really raggedy if needed. I really enjoy his portrayals. Makes any drama have just a wee bit more ZING. the man has the skills!!
Yamamoto shows that he doesn't need main roles to shine! He's one of the best actors I've seen, doesn't matter whether he has a main role or supporting role.
Just watch GTO for example and you'll realize how much he does for the drama!