No matter what role he played, Lorenzo Music just somehow made it his own--even though it always sounded exactly the same; it was his role, & he was meant to do it.
When Music's Venkman was a jack@$$ to someone, you still sympathized with him because he had a certain humaneness in him; you may not have agreed with his decision, but understood where he was coming from because he put so much depth into the role.
I know people say that Coulier was brought on to sound like Bill Murray, but the big problem with that is even Murray had that humility to the role which made his Venkman really likable.
The only thing Dave Coulier brought to the role was sorta kinda sounding like Bill Murray. He didn't have the heart in it, sounded like a parody of a California surfer, & when his Venkman was being a jack@$$ it was just that; you couldn't even sympathize with it.
Dave Coulier almost sounded like a kid-ified version of Venkman. He was just....terrible...as Venkman.
I think even the Nostalgia Critic said it best: "man of 1,000 voices..and absolutely none of them accurate!"
I remember while watching the interviews on the RGB DVD set, Kath Soucie mentioned that while waiting for his cues, Dave Coulier would be in the back of the room entertaining himself with his cheezy little voices....
to which I must then comment "well, ya might as well entertain someone with 'em, even if it's only yourself!"