I dunno, as far as I can recall the book was pretty goofy too. That's one of the things I was hoping Jackson would make sure to do with the films, rather than making it broody mcbroodwalking like the LotR. That said, I do think the goofiness was over the top, as you say, but I definitely don't think the goofy atmosphere is a flaw or a bad thing. I liked the whole barrel section, it was one of the less boring parts of the film. I remember finding that part funny in the book, though I might be crazy, so I'm glad it was equally as silly in the film. I loved Bilbo's moment of realization after he pushed them all off into the river.