In “The Unbearable Weight of Massive Talent,” Nicolas Cage plays Nicolas Cage, a conceit we get used to in a matter of seconds, even as it turns into a gift that keeps on giving. There’s a reason we get used to it so quickly: Movies with a meta dimension have been with us for years — movies like “The Player,” where Robert Altman cast a galaxy of Hollywood stars as their real-life selves, or “Being John Malkovich,” where John Malkovich played John Malkovich, or “Adaptation,” where Cage played Charlie Kaufman, the screenwriter of the film we happened to be watching. Unlike those movies, “The Unbearable Weight of Massive Talent” isn’t a floridly ambitious pretzel-logic art film. It’s a commercial comedy that has a delirious good time poking fun at Nicolas Cage, celebrating everything that makes him Nicolas Cage — and, in the end, actually becoming a…
