None of this is particularly difficult to play (that is my impression as a pick player at least, I find someone like Jack Bruce or John Entwistle harder to replicate from where I'm at), but it's idiosyncratic in its up-frontness. Or: Intrepid to be heard. Much of his inimitable style has to do wit the fact that he's pretty much always ahead of the beat. Don't think he would have lasted long as a bass player for a laid-back rhythm section a là Bad Company or Steely Dan!
Should be mandatory listening for young bass players today. I'm not much of a Yes-man, but Squire's lead bass playing always brings a smile on my face.