Must say, this wasn't all that funny for a Woody Allen movie. Not that it wasn't, but it was slightly more serious but not uncomfortably heavy.
I think when Woody Allen thought about the script, he was under depression and had many thoughts running in his mind. The movie has many themes, each quite suitably handled by the actors.
Hannah's husband Elliot gets entangled in a relationship with her sister, Lee. He seems to have lost it for Hannah because of self-sufficiency and resentment of her emotional strength (picked from Wikipedia). Lee, herself, is living-in with a reclusive artist, Frederick. And seems like she has lost it for him as she doesn't feel equal.
Then there is the third sister, Holly, who is not too sure what she wants in life. She is contemptuous of Hannah despite the financial dependency.
The only comic relief in the entire set-up is neurotic Mickey, Hannah's ex-husband. Of course, Allen plays that role, so you can be rest assured that he is funnily irritating. Now, his part in the movie explores life, death religion and spiritual awakening.
It is a typical Woody Allen movie, albeit a bit serious.