But seriously, I kind of agree with earthman, the main reason he was "innovative" was that he was better than pretty much anyone else around at the time. Nothing I ever heard him play was really all that different from the blues rock that preceded it but he could play faster and was on drugs a lot so he had a tendency to play with the whammy bar. His sound was more distorted than most other people where playing with at the time which let him play faster and whatever. It really wasn't all that much about speed but the point is he was innovative in that he was one of the first really technical (not by today's standards but still) guitarist and was also a pretty good song writer.
I think a lot of it was timing too, as it normally is with legendary people. He exploded at just the right time and died before he could fizzle out.
There were arguably a lot more innovative bands and guitarist out there at the same time though. Hendrix's music isn't really all that relevant anymore, I mean he influenced probably all of rock but now that influence is mostly second generation or even third and the people who do have him as a major direct influence sound old and out of date. There were a lot of progressive and psychedelic groups from the late sixties who are just now or in the past 10-15 years becoming relevant to modern music, and guitarists who's playing can still inspire relevant modern music directly.
Hendrix was an innovator but like Earthman said it really isn't separable from his skill as a guitarist because what he was writing wasn't really all that ground breaking (in the context of history), it was mostly the way he played.