Clooney was supposed to be wooden and stoic, thence the humor in the movie.
Having said that, he has no more range than Pacino.
I agree; however, others did the rigidity thing so much better, such as Ray McKinnon, who played Vernon T. Waldrip:
BRW, you are right on the money about Pacino, another one-note guy. Think how much better Scent of a Woman could have been if only the right guy had played the role -- Robert Duvall. A tragedy. Duvall even knows how to tango, having an Argentine wife. Wonder if he turned the role down, as too much like The Great Santini?