Funny you mention that Billy, when Harris interviewed for the job, he said that Irwin Allen was a total ass full of himself, a tyrant, and he fought with him to make the Smith character the way he did, as well as making him a "special guest star." Allen hated it and him, but Harris was right and it made the show the success it was. Otherwise, Smith would have been a typical 2-dimensional villain and hated, and the show would have quickly become stale, predictable and boring.
Because of Harris' vamped up Dr. Smith character, LIS not only was a big hit, but really, the only real hit Allen had out of several series including Land of the Giants, The Time Tunnel, and Voyage to the Bottom of the Sea (which wasn't bad the first year).
I actually still remember being over at a friend of my mothers as a little kid and watching the premier of LIS the night it first aired on their TV.