Tonally erratic but chock-full of interesting concepts, Bobcat Goldthwait’s World’s Greatest Dad packs a lot in its 99 minute run-time: depictions of loneliness, teen rebellion, and whether the doors of opportunity that tragedy can open—and not just the selfish sort—are worth sacrificing your ordeals. Too much plot summary in this capsule would spoil the key plot twist, but World’s Greatest Dad centers around Lance Clayton (Robin Williams in his Dead Poet’s Society / Good Will Hunting / One Hour Photo serious mode), a teacher and single father whose teenage son Kyle (Daryl Sabara, previously best known for a guest appearance on Showtime’s Weeds) is a sex-obsessed, foul-mouthed loner who has no qualms cursing out his father when he doesn’t get what he wants or snapping cell phone photos of Lance’s “TILF” (Teacher I’d Like to Fuck, in Kyle’s words) girlfriend Claire (Alexie Gilmore). The worthlessness that Lance feels as both a human and a father slowly morphs into self-discovery as World’s Greatest Dad evolves, and there are many touching moments: hell, some are downright sad, both in the rapid-fire first half and the unexpected second. And the deadpan, dark humor also sometimes hits its mark, providing some surprising laughs. However, World’s Greatest Dad is all over the place: it often goes from amusing to depressing in the matter of seconds and then abruptly switches back, preventing the viewer from getting into any sort of rhythm. And some of the little touches just don’t work: Lance & Claire’s fruit-based pet names for one another quickly grow irksome, and the relationship between Lance and Kyle’s best friend Andrew strains believability in the film’s second half. All in all, there’s a good deal to recommend here (the music is also very well utilized, though there’s not much visual spice), though the final vessel is certainly flawed and could have been much more powerful with a disciplined hand at the helm. But then, given that World’s Greatest Dad was directed by a former comedian, the end result is about as good we can reasonably expect.