What is the theme of Garden State?

I haven't watched the film in many years, but Wikipedia does supply a paragraph on the film's central themes

The protagonist's father has been "protecting" him from his own feelings with pills, namely lithium carbonate, which are seen "as the symbolic soul-destroying enemy". Zach Braff describes the themes of the movie as "love, for lack of a better term. And it's a movie about awakening. It's a movie about taking action. It's a movie about how life is short, go for it now. My character says, 'I'm 26 years old, and I've spent my whole life waiting for something else to start. Now I realize that this is all there is, and I'm going to try to live my life like that'". "I have this theory that your body goes through puberty in its teens, and the mind goes through puberty in your twenties," he says. "[Andrew] is dealing with issues that you are going through all the time going into your thirties. He's lost and lonesome, which is something I definitely felt in my twenties".

So ultimately it's a unique coming of age story about not taking things for granted and learning to go after the things one wants, because life can be too short.

More specifically one internet commentator from DSQ (Disabilities Studies Quarterly) looks at themes stemming around happiness in terms of normalcy vs abnormalcy and/or how flaws are authentic and make humanity "real" and therefor the film may be about a celebration of individualized uniqueness...

One of the main themes of Garden State is the idea that happiness can be sustained only by money, a series of drug or alcohol-induced quick fixes or, in the case of Largeman's father, Gideon, by a constant, self-regulated insistence on normality. In this world, where everyone is searching for his or her own version of the good life, "normal" and "abnormal" are often subverted. While Largeman's father, as a "normal" and privileged psychiatrist, is portrayed as cold, disconnected and somewhat abnormal, his son's ability to play a "retard" so well that no one can believe that he is "not really retarded" (in LA, Largeman was an actor known for such a role) represents mental disability as a "normal," even desirable, subject position. As Sam stresses, what is important is not being "normal," but being "real." From this perspective, retardation and high intelligence are just two points on a continuum that strive not for material, rational or "stereotypical" perfection, but for unique moments of imperfection that are revealing of our shared, vulnerable, and decidedly imperfect humanity.

In troubling our notions of normality, Braff makes an admirable attempt to valorize the non-normal, the different, quirky and unique individuals and individual moments that make it okay to be "who we are." Central to this theme is Sam, Largeman's girlfriend. Sam, who has epilepsy, insists that it is her difference, and her ability to create an original moment, that keeps her happy and makes her feel unique. Here, uniqueness is not a vague concept, but a way of being; it involves "discovering something, doing something," constantly seeking after difference rather than sameness. Whether it involves "screaming over the infinite abyss," winning a "retarded Oscar," or doing something small, uninteresting, and seemingly pointless, it is important, this film appears to say, to remain true to one's difference, however that difference is constructed.