Greenberg: A film about (doing) nothing

Here's what we know about Roger Greenberg.
+ He's just been released from a mental hospital.
+ He functions — sort of — on a cocktail of pills.
+ He lives in New York, but is house-sitting in Southern California.
+ His college rock band was about to sign a record deal when he backed out.
+ He doesn't know the name of his best friend's son.
+ At the moment, he's busy doing nothing except writing letters of complaint to Starbucks and American Airlines, a pet taxi and Mayor Bloomberg.
And in this eponymous movie, he's played by Ben Stiller, who's superb as a 40-year-old narcissistic, paranoid, anxiety-riven, socially inept Peter Pan.
Greenberg, the man and the movie, are both sad and funny. Movie-goers will laugh, not at him or with him — he's not laughing — but because we see something of ourselves in this lost soul, and because we know that at least some of his nuttiness is a sane reaction to an insane world.