One sentence verdict: this film is an honourable miss. A man's reach should exceed his grasp, and I'm pleased to see Gervais, who is a very clever man, reaching towards a metaphysical comedy-drama like The Truman Show or Groundhog Day, but to be honest he misses that standard by miles. The film plummets at the end into Hollywood claptrap, but there's a lot on the way that is pretty good: jokes that make me laugh, pathos that made me cry. But it doesn't quite hang together.
Many of the best popular films of the past twenty years or so hinge on a breakthrough of understanding. The Shawshank Redemption, the Usual Suspects, The Truman Show and so on. Gervais tries to do this, as his eyes are opened to the infinite possibilities of fiction. But he can't act it. It just doesn't work. What a shame.
However, at least he knows what he's trying for, and I hope he'll try again and perhaps make it next time.