Well, i'm not sure why I like the Poppers so much, it was probably just the idea that former child stars could retain their child-like sort of psyches for an indefinite amount of time. They might have five-o-clock shadow, but somehow they're still just kids. It's almost a tragic statement on the effect Hollywood has on some people. Besides, those catch-phrases are... well, I like em, for some reason. If they stayed around but didn't take precedence on-screen then it would be fine. Their appearance in episode 2 was executed just fine.
Sybil Pandemik, though, is another favorite of mine. The voice and character design go perfectly together, and her personality quirk is charming (hey, maybe her conversations with Sam and Max will inspire her to become a Freelance Police Officer, so the two businesses would have to compete

) I plan on doing fanart of her sometime.