Lomu was one of the greatest backs to the play the game in my lifetime if not the greatest, not only did he have size and speed he also had what Peat mentioned above - Agility and those 3 things in combination made him and his style of play at the time unique.
The agility is often overlooked but just as important, his ability to change direction and accelerate again stopped him being just a big
"go forward run straight tractor" of a player, instead he was something very special
No one had seen that combination in a back before to such an extent
Its hard to conextualize that now in the fully proffesional era were large wingers/centres are common place.
Lomu was a game changer in every sense of the word