Want to know if someone is a really good voice actor? If they can do a character doing another character (or voice). Homer in this clip sounds a lot like Homer Simpson doing a bad impression of what he somehow imagines mr. Burns sounds like. There are better examples of this in the Simpsons but my point stands.
I know this has been mentioned here before but the visual jokes that appear in the Simpsons, usually in the transition scenes, are a large part of the charm of the show and why I still enjoy rewatching the old episodes.