It's because he adds too many ruffles, creases, crevices, etc. to a fairly plain art style and colour palette. It ends up clashing as well as making everything look kinda' dirty.

reminds me of old-school furry porn. that real usenet shit

It's like a shitty copy of the style of Marmaduke with terrible punchlines

I've always liked it. It's expressive enough for political cartooning and RBS has a pretty distinctive style that makes them stand out enough to be recognizable.