Yeah, Dana was in the 1st episode as Garys living ex-roomate.. and was not funny. It was dissapointing.
But he's been in it in Season 3 as a demon, and it really works!
Everyone in the show is funny, they just all have funny-bones. And the show is written in such a way that the plot is just a paper thin excuse to have the characters stand around saying funny stuff and have funny things happen to them.
In that respect, the general writing structure reminds me of 'Aqua Teen Hunger Force' a lot, except 'Your pretty face is going to hell' is tighter.