oh sorry..i thought you talking about air zonk since the beginning, since i wasn't enough aware of the US pendant names.
so what you're saying is, that PC Denjin (air zonk) had impressive BGs, while its sequel CD Denjin (Super Air zonk) disappointed you in that matter. now i can agree with you
although CD Denjin has also its very nice and colorful BGs here and there (e.g. beach level).