Solaris

Like many works of classic SF, it helps to put this in the context of its time and remember what had come before. With this perspective, it’s clear just how ground-breaking Solaris was - a huge idea, realised in grimy and convincing detail. You can draw a straight line from this to Neuromancer (or just about anywhere else for that matter) - a disembodied, unknowable intelligence that one interfaces with directly in a reality that is fully real despite being manufactured.