Kyle is an obnoxious teenager. Not in the 'troubled soul struggling to find himself' obnoxious but in the sense that he totally without redeeming features. His favourite past-times are masturbating, thinking about masturbating, obtaining material for said hobby, and treating his father (Lance) with a complete lack of respect. Robin Williams plays Lance who spends his days alternating between being a failed writer, trying to make allowances for his wayward son, and a teacher whom secures little respect. Lance's only respite from his drudgery is his love-interest with a colleague, clearly punching above his weight.
All this changes when Kyle meets a sticky end after a auto-erotic asphyxiation attempt cuts short his shallow life. Apparently to avoid the ignominy of having his son found like this Lance makes the death look like a suicide, complete with profound goodbye note hinting at a deeper despair hidden from his peers. This decision then has a domino effect on Lance. Kyle's school comes together in united grief, students and staff alike eulogising this talented and promising alumni cut down in his prime. From there of course, Lance's lies spiral out of control gaining a momentum of their own as you just know this can't end well.
What worked well about World's Greatest Dad (irony of the title not lost) is that most of the cast are no better than Kyle; rather, at least Kyle didn't pretend to be anything other than obnoxious. It's almost a moral parable, what motivates people (although superficially altruistic or noble) is often borne out of self-interest; 'what can I get out of this situation?'. Also that somehow death magically confered the deceased with attributes that were never there in the first place; all wrongdoing cleansed. I assume it's meant to be so insomuch the assembled malingerers and hangers-on desperately want to believe the fantasy (former) life that Lance has painted so they can buy-into the grief; it's laughably pitiful and a real sideswipe at their hollow grief.
Williams shows again that, in my opinion, he does best when playing it straight and here he is no different. Supported by a very able assembled cast, Williams plays Lance well as the sad-sack father and teacher who strives to be a good person who can't help but capitalise on a twist of fate that promises him a better life. In short, an enjoyable watch which pulls no punches in its subject matter. Plus, I imagine Daryl Sabara had a whale of a time playing Kyle; I bet he couldn't believe his luck when he saw the script.