It's a well-travelled path: a flat-out comedian wants to be taken More Seriously As An Actor, and so gets into a movie that allows him to show that he's more than Ace Ventura/Carl Spackler/Happy Gilmore/Austin Powers/Mork/Navin Johnson.
This is one of those, as Will Farrell plays IRS auditor Harold Crick as an introverted, friendless, nearly invisible non-entity; totally different from Ron Burgundy or Ricky Bobby. Supernatural complications ensue when a reclusive novelist (played by Emma Thompson) somehow includes Harold as a doomed character in her latest book, and he can hear her narrative voice as she moves his character through her plot.
I can hear you saying: sounds as if it's a cynical mutation of Groundhog Day. Kind of, but it's pretty good anyway! It helps that Farrell is surrounded by a supporting cast that ranges from very good (Maggie Gyllenhaal, Queen Latifah) to near-immortal (Miss Thompson, Dustin Hoffman).
One big problem is that, while Thompson's character is described as a literary genius, and her novel described as her potential masterpiece, the actual excerpts we're exposed to over the course of the movie are pretty dreadful. (Yes, I was able to suspend disbelief for everything else, except that I couldn't imagine anyone would think that was good writing!)
Trivia: Tom Hulce is also in this, his first non-Quasimodo movie since 1995. He was unrecognizable (but very funny); when I saw his name in the credits, I had to click back to his scene. "Oh, yeah, that's him… wow, he's changed."