Robert De Niro and writer-director Paul Weitz find the most congenial material either of them has had in quite some time in Being Flynn. When it sinks in after a while that this film actually provides a meaty, serious role for De Niro rather than just a cameo, you wrack your brain trying to remember the last time the actor had a really good lead part in a quality movie. The answer is, probably 17 years ago, in 1995, when both Casino and Heat came out. Shocking, but true. It's also the case that De Niro, playing crazy old Jonathan Flynn, who claims that he, Mark Twain and J.D. Salinger are the only great American writers, gives an honest, vibrant performance after an overextended sojourn through paycheck territory. Happily, he's got a splendid counterbalance in Paul Dano. The sources of the film's gratifying equilibrium would seem to lie equally with the carefully balanced structure of Weitz's script and Dano's restrained but open-hearted performance. De Niro supplies the volatility associated with the Elia Kazan school of acting, but Dano refrains from responding in kind, offering an unusual sort of serene transparency that is not only dramatically effective but quietly suggests the nature of a thoughtful formative writer digesting life experience for future use. Badly Drawn Boy, aka singer-songwriter Damon Gough, provided the effective musical backdrop for About a Boy, which Weitz co-directed with his brother Chris in 2002, and does the same here with an engagingly offbeat selection of songs. Declan Quinn's sharp cinematography and Sarah Knowles' attentive production design, linked to New York-area locations (Flynn's memoir is set in Boston), are major pluses.