[quote=@Roosan]
Grevious actually wasn't force sensitive, I believe. He was just so heavily modified, so angry and so skilled he could compete with Jedi at their own game.
[/quote]

Yeah, I think I remember reading something on a forum that claimed he was using enhanced droid reflexes and calculating abilities to substitute for the Force awareness that keeps Jedi from cutting their own limbs off with a weightless weapon, as well as fight on equal footing with multiple Jedi at once because his computing ability was so advanced. And of course the whole four limbs thing.