Seemed like a decent sort of guy, too, from what I've seen of his interviews and clinics. I attend one of his clinics in Long Island, and he was open and friendly with everyone - certainly not some arrogant jerk - which are usually the MEDIOCRE players, come to think of it.
I saw him play a couple of times. At one concert, there was some kind of problem with the sound, which he wasn't happy about. The music ended and I heard him "and THAT'S ALL I KNOW!" He then shrugged and moved on to the next tune - the show must go on and all that.
Allan is a real example of artistic integrity - he always stuck to his guns, and hated it when record companies tried to pair him with musicians he didn't want to play with and simplify his material so as to make him a "star".
So his legacy will mostly be that lots of guitarists (and others) put him on a pedestal!
Like Frank Zappa, who called him "the most interesting player on the planet", and Eddie Van Halen who said that Allan Holdsworth "is the best in my book". Robben Ford said he was a "monster", presumably in a musical and not personal sense..... And a lot of jazz players have said he was a very fine musician.
Recently I heard an interesting piece where he played with saxist Wayne Shorter (Miles Davis, Weather Report) - those interested can google "Allan Holdsworth with Wayne Shorter" on YouTube. Their sounds blended beautifully!