I agree with another reviewer, you do have to have lived a little to fully appreciate this film. If you have ever experienced rocky highs and lows, then you may well find something here for you. You don't have to be male to appreciate the struggles and poignancy contained herein.
All the characters are simply superb. Anyone who has felt on an emotional rollercoaster for whatever reason, will be able to feel for, as well as laugh with, the character Miles, who is played so superbly here. There is plenty of pathos and laughter to be found here, and the ridiculousness of the human condition is laid bare without the usual Hollywood gloss. Virginia Madsen is also simply wonderful in this. I finished watching this with a real regret that I would see no more of these wonderfully flawed and rich characters.
There are many moments in this film that are funny. The humour is in a recognition of our own humanity at best and worst. To see Miles (Giamatti) act as a man on the edge is a joy to behold. His loss and rejection reflects the difficulties we all face, and I like that the film deals with this in a very `un-Hollywood' way. How one moment we can lose it and feel utter despair, but, how we can be coaxed out of this a few minutes later by a good friend to feel something encroaching on normality again. This is a film that I will gladly watch again and again.