If I can clear a few things up for you...
I'm no real authority on humor, so instead I want to take a constructive approach to understanding why you've gotten mixed reviews.
Ok, to get the more painful part of the review out of the way: the reason you are getting the negative reviews is because of the production value of this piece. It's not that it blows or anything, it's that you're clearly a person who prizes concept over delivery. People will complain if they have their lobster served to them on a dirty plate; people will complain if your comedy is overshadowed by lesser artwork. The complaints you're getting target your audio and visual quality, and because it stunts their appreciation for the jokes themselves, they gripe about the cartoon being unfunny. It's unfortunate that visual appearance has everything to do with delivery of comedy, but it's true.
On the other hand, people like Tom can see through to the meat of a person's creativity because they've seen it all before: good, bad, whatever. Graphics and production are much easier to improve than a sense of humor, so you're on the righ track. None of us started in Flash knowing what we were doing.
I'd say you should build on it. Don't change your style, but work on those backgrounds, walkcycles, human forms, etc. Or don't...you'll still be funny. This is more a suggestion of what to do to avoid those negative reviews than it is on what you should do with your own work. That's not for me to say.
-Swain