It's been quoted several places that Bruce's forte was in taking something someone else did - doing it just as well the first time he tried it, and better the second go around. He was a phenomenal natural talent - but he ultimately left behind no "system" of teaching - much the same as when Ed Parker died. There were so many different evolutions of Bruce and Ed's work that finding one specific way to do things was no longer viable as a training methodology. Witness the various JKD "seniors" and the various Kenpo "seniors". They all move and teach differently. All of their students move and teach differently. (Generalities for the sake of argument - there are specific lineages that all move the same way. Stay on topic people.

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Bruce was a major force in the martial arts - his greatest legacy was the upheaval of "traditional" ways of thinking - and taking a piece from here, and a piece from there to use for your own. The downside to that methodology is that Bruce was one in a million physically who could do that. I've not yet seen another who was able to put things together across a varied spectrum of styles. Was Bruce the "greatest" ever - I disagree with that assessment.
1)Bruce left no "system" - but a philosophy. Was he a pioneer - yes.
2)None of Bruce's students move like Bruce did.
3)And the vast majority of people cannot benefit from studying and choosing pieces of style x, y, and z because the vast majority do not conceptualize the How, Why, and Purpose behind the various concepts of style x, y, and z in such a short period of time.
Was he overrated - Who cares?