A lot of the appeal is aesthetic / stylistic. Yes it's "hard to read" compared to more "traditional" works, but it has its own unique appeal... an appeal that resonates with some people and not-so-much with others.
Another part is that Gibson was the first to put together cyberpunk as a genre and an aesthetic and a little dystopian futurism. It was truly the first that spawned a number of now familiar ideas like AIs battling firewall and attack and VR as a UX method.
