After viewing the film, I can honestly say that not only were these critics absolutely wrong, but they are, well... just absolutely wrong. Hesher plays like an anarchist's re-telling of Mary Poppins: When a wife/mother of a relatively normal pairing of father and son dies in a car crash, the only person who can lift these two mourners out of their depression is a crude and impulsively violent metalhead.
While I expected Joseph Gordon-Levitt's performance as Hesher (the metal head) to be the highlight of the film, I was pleasantly surprised for it to be Rainn Wilson of The Office fame. His performance as the pill popping Dad is a subtle gem. Despite his dialogue never really going beyond a few sentences at a time, you can never take your eyes off him. Rainn Wilson brings truth and meaning to every scene, and truly is an overlooked marvel in this film.
Though Rainn Wilson had the better performance, that does not exclude how well Hesher is played by Joseph Gordon-Levitt. In what is obviously a deep departure from the roles he is used to playing, Levitt makes Hesher a disturbed, but oddly sympathetic character. While his scenes with T.J (played by Devin Brochu, in a weak performance that will not be regarded in this review) are filled with fear, the scenes with T.J's grandmother contain an odd sweetness. Think of Hesher as like a more violent Jay from Clerks or Dogma.
Even more surprising than who the strongest performance in the film belonged to, was who the weakest performance in the film belonged to: Natalie Portman. Moving from the success of Black Swan to a series of duds (No Strings Attached, Your Highness, Thor), I have no idea what Natalie Portman is doing. She already proved to us that she can truly act and received an Academy Award for it, so why has she been doing so many phoned in performances lately? Here, she plays a supermarket worker with incredibly low self esteem, but Portman plays this character like a female depressed Woody Allen. This would've been more forgivable if an actor besides Portman was in the role, but because it is Portman, I expect a lot more.
Hesher is a surprising gem in the world of pointlessly quirky independent films. With an interesting plot, well thought out characters, and mostly good performances, Hesher truly is an underrated find. If you have Netflix, it should definitely be sought out.