How anyone can consider him entertaining is beyond me...
"He found something that he wanted, had always wanted and always would want— not to be admired, as he had feared; not to be loved, as he had made himself believe; but to be necessary to people, to be indispensable."
-F. Scott Fitzgerald's This Side of Paradise
I would actually be curious to see him onstage. His on-screen energy/persona can be rather oppressive and heavy, but the same was often said of Bert Lahr, and I kind of feel Nathan Lane can sometimes run that way as well. Not to say Jack Black is anywhere near as talented as either of those two, but I wonder if he would fare better with a touch of distance and reality between him and the audience, not magnified to the degree that he is in the movies.