I adored him in Mork & Mindy. It was clear that he was improvising and riffing parts that were not scripted - a lot of that was lines that would only appeeal to, and be understood by adults watching, such as his (perfect) impression of Jack Nicholson.
Another example of that razor-sharp improv. skill was when he was given a line about how could an alien come to earth, to which his response was "How could an actor become President?"
I found his films mixed, but he was always varied, and pitched his acting to fit in with the roles he played.
I think his loss, like any loss to suicide, is a tragedy.