The set up is a simple one - take a 40-year-old guy who has been exiled to New York for the last 15 years and then have him return home to LA. This allows the gentleman ample time to contemplate who he is, who he was and all kinds of other navel contemplations.
In Greenberg, Ben Stiller is the 40 year old, and for the most part the film does a fair job of mining those contemplative possibilities as he re-connects with old friends and romances. Unfortunately this is not the only theme of the film and it is the other theme, that includes one of those wacky, made in Hollywood kind of disassociative love stories - you know the type, where odd wacky girl is, for god knows what reason, smitten by our hero, even though he's a self centered ass who appears to have no respect for her feelings, or her person. Ah, but love conquers all - yep, this film has a bridge to sell ya, and it doesn't help that Stiller is recovering from a mental breakdown, and as such gets a big get out of jail free card - it's as if he has carte blanche to be a jerk and then everyone just smiles and gives him a pass because he's "troubled".
The direction of the film is adequate as far as it goes, trying to keep the script interesting while juggling the two themes. There is even a supporting character, that of Stiller's old best friend, who provides a moral center to the film - playing a man who had grown up and moved on and is already content with the person and life he has found - something that Stiller is still grappling with (hence the aforementioned breakdown).
If the film had only focused on these ageing and self realization issues instead of investing so much face time to the romance, it would have played much better. But alas, the romantic theme is front and center - to the point where the quirky, much younger female (played competently by Greta Gerwig) is the one on screen during the first fifteen minutes of the film - as if to say "yeah, we know that the name of the film is Greenberg, but it's really about this girl.
The girl unfortunately is more of a nut job in her own way than Greenberg - I guess the message was that she was supposed to be adrift in life as well, but gee golly, that's just what I wanted to see - two slightly crazy people falling for each other - doesn't it just tug at the old heartstrings? The entire romance would have been ok as a background bit on the road to self-discovery, but I felt it got in the way of the much more rewarding theme.
For example, there is a wonderfully done scene where Greenberg tries to re-connect with an old girlfriend. He tells her a story from his point of view concerning an event that happened 15 years earlier - it is obviously very important to him, as he remembers the smallest of details. But when he apologizes for hurting her over said incident, she looks at him oddly and then confesses that she doesn't remember the incident at all. Man, I've been there - something that was a very important event in my life, and something that I thought I had shared with someone special, I later found out wasn't even a blip on her radar screen- and yet conversely there were things she remembered fondly that I had totally forgotten. This was a powerful and true observation, but then the film mishandled the conclusion by having Greenberg hit on the girl in spite of all the evidence that their prior relationship was much more important to him than it was to her. And of course all this was in the middle of Greenberg's sorta on, sorta off relationship with Gerwig.
I suppose the ultimate message here is that we're all searching for connection - with our self and with others; but in attempting to tie it all up with a nice happy face and a "I'll settle" kind of love, the film failed in its attempt to truly soar.
One final point - Gerwig slouches through the entire film - whether this was her attempt to portray a younger, more uncouth woman, I still felt like yelling at the screen "stand up straight!!!"