Faux-profundity wrapped in a thousand onion layers of excruciatingly clever, obfuscating obviousness. In other words, it's not just a Charlie Kaufman movie, it's a Charlie Kaufman movie without the filter of a more restrained director (and when Spike Jonze counts as "restraint" you should seek help).
I won't bother trying to tell you what this movie is "about". If you've seen it, my previous paragraph says it all. If you haven't, nothing I write will ever explain it.