Before I get into the extras on the World's Greatest Dad DVD, here's a bit from I'm re-running from my original review:
"Robin Williams and Daryl Sabara are paired magnificently here, with Sabara surprising me the most with his portrayal of the world's worst kid. Kyle (Sabara) is the living embodiment of the mallrat mutants that make people not want to leave the house anymore. Everything is "gay" and "stupid" to him, and he has no concerns but his personal obsessions."
The brilliant Daryl Sabara, playing much more immature and toxic than he is in real life. It takes a brain to play a sleaze well...
"Lance (Williams) is stuck with this cromagnon in a boy's body for his son, a beautiful girlfriend who doesn't want their relationship to be public, and diminishing attendance in his Poetry class. Lance is an aspiring writer who's never gotten noticed or published in a big way, and he's trapped on all sides until something terrible happens, offering him an escape at a cost. This inciting incident doesn't happen until a ways into the movie. Perhaps it's been spoiled for you already, perhaps not. Either way, I refuse to specifically spoil the tragedy that befalls Kyle's dad. It's hilarious for only an instant, quickly turning heartbreaking and soulful."
"That is the very moment many will discover that Bobcat Goldthwait is a truly gifted director and storyteller. With no qualifications, I feel that after this and Stay (retitled Sleeping Dogs Lie), he's one of the most talented auteurs we have discovered in the first years of this century. I'm convinced that had he let any studio or backer muscle him around, the movie would not be so wholly satisfying. The fact he stood his ground is a rarity in an industry of complacency and kiss-asses."
The DVD & Blu-ray features a few deleted scenes (but more notably outtakes) among other things. The best piece in there is the behind-the-scenes featurette that runs about 20 minutes. The catch some nice moments from the final day of shooting in particular. The commentary with writer/director Goldthwait is really excellent. He mentions this, but you can tell that he listens to a lot of commentary tracks himself. A music video and an HDNet featurette round things out.