I always saw him as more of a percussion player that happened to use a bass. His style is as dependant on muted percussive slapping as it is on actual notes.
It's a style and sound I don't like at all, but to Fieldy's credit, it worked extremely well for Korn and inspired a hell of a lot of kids to pick up a bass.
As an amusing side note, I once ordered a copy of his legendary solo album 'Fieldy's Dreams', to see if it was as awful as it reputation would suggest (it's worse). Not only did it cost me 1p new, the seller sent me two copies and a radio promo disc. Seems he couldn't get rid of them quick enough.