It's not that the designs were *bad*, just that they were hardly mind-blowing or complemented the series. Gen V's starter designs were just lazy too.
In generation IV we had Chimchar -> Monferno -> Infernape which was a lovely Fire/Fighting monkey type thing.
In generation V we had Tepig -> Pignite -> Emboar which was...oh. Another Fire/Fighting, and looks slightly similar...
You then have Gen V's
ice cream pokemon, a badly named pokemon called "Beheeyem", for goodness sake, and really, I just didn't feel it. My main gripe about Gen.III was really the legendaries, that adopted a very blocky look. Everything had sharp angles and looked like it was computer generated, not really natural.
I realise I'm probably the only person in the entire world who thinks this.