The SF premise isn't unique (although it pretty much was back then), but the focus is a completely different one than in other artificial reality films. Especially during the first part it is an elaborate crime picture, that uses the SF premise to tell an unusual crime story in which the forced detective tries to solve a mystery with the obstacle of vanishing characters and unhelpful witnesses who don't have to lie to be unhelpful. Instead of an unreliable narrator we have an unreliable world.
In part two we follow the main character's struggle for sanity and it turns more into a psychological examination of a character in an extreme situation. He knows his very existence is nothing more than electrical impulses, how does he deal with this knowledge? He knows that there is a world that is more real than his, but he is trapped in an artificial world, a world where nobody can understand him. The problem of thinking of knowing something essential about the world that nobody else knows or wants to believe is a very real one that many of us can identify with. For me the film transports this hopelessness very well, with its dreary, artificial atmosphere which also supports the factual artificiality of the film's world.
Other than 'The Matrix' or 'The Thirteenth Floor' it's little concerned with evoking a sense of awe for its artificial reality plot, instead it very much focuses on the psychological aspects. Philosophy is only in so far interesting in that certain philosophical concepts are essential in how they shape and alter the character's perception of the world.
Arguably it is longer than it has to be (which isn't a problem if you are as captivated by it as I was) and part 2 runs pretty low on steam.