I liked him for his ad-lib comedy. I came across this clip when the BBC were taping a TED conference broadcast and something went wrong with the technology. Robin Williams piped up from the audience with "“Why, at a tech conference, is everything run so shittily?" and then proceeded to get up on stage and amuse the audience for a couple of minutes https://www.youtube.com/watch?v=_q790fmirQk
https://www.youtube.com/watch?v=_q790fmirQk