Does anyone else feel that the Herman Munster character not only changed emotionally, but physically as well?

I think there was a change in makeup artists. Read it somewhere. The later makeup really doesn't make him look as scary. Eeek, look at him in his original makeup in my avatar.
And you're right, there was that change in Fred Gwynne's portrayal.

I think there is a big change in the whole series between the Beverly Owen episodes and the Pat Priest episodes

When I get Season 2, I'm going to take a small picture of Herman, from every single episode, and then we'll really see the change.