For me, he is so incredibly important because he could do whatever he wanted.  He exercised complete freedom in his work.  When I saw the Guggenheim Retrospective in 1997 (so large that it filled the museum's midtown and SOHO locations), I was completely blown away.  It was then that I realized all the stuff that people were crowing about in the 90's ( collaboration, performance, expanded painting, technology, mediated imagery, working outside of the rectangle, graffiti, symbolism, painting as language, politics, multiculturalism) had been part of his practice from the beginning.  And the " Erased deKooning Drawing" is still one of my favorite works of art of all time.