Let's just say putting the letter D in the title was not the best grade for this would-be growing-up nostalgia. It's got enough jumbled-up, lurid melodrama for several plots. It's framed as sort of a love note of wisdom, maturity, and advice for Tom's son (although the sleeping kid doesn't have to hear all this. Alas, we do). If any of the film's tearjerking pathos were believable for a minute it would be, well, unbelievable.
Anton Yelchin doesn't look or talk like an idealized, movie-cute child star, so picking him to embody the awkwardly precocious Tommy is one small virtue. Oddly, there's a certain family resemblance, facially and in the contrived snappy banter, between him and Robin Williams, who gives an unconvincing portrayal as Pappass, with excessive mugging and doubletalk. It may be significant that the one family in the whole movie that looks intact and functional -- father, mother, child -- is that of that of the adult Tom, over in Paris. How he got to that state of contentment, after such a turbulent adolescence, might have made a more interesting story.