World class wrestling, the best TD defense in MMA, strong kicks and a great jab. Let's not forget that GSP was the most well rounded fighter in MMA and:
Submitted prime Matt Hughes and KOed him with a head kicks
Dominated one of the most decorated wrestlers in MMA, Koshchek
Beat prime, juiced, Muia Thai monster, Alves
Dominated prime Condit
Dominated prime Fitch who beat (Hendo, Maia, Woodley, Lawler, Daley)
Walked through prime Nate Diaz
Submitted Bisping the 185# champ
He defended his title 9 times. I think Prime GSP matches up pretty good with most of todays welterweights, to think otherwise is naïve.