For one thing, the protagonist is no longer trying to kill himself.
(Not until after the holidays, and reality sets in, anyway…)
That said, the main reason the film is not seen as depressing by modern viewers is that it wasn’t filmed more recently. A color version with the current field of acting talent would produce either a much more truthful/depressing version of the film, or one seen as far less entertaining in it’s sugar-coating of current economic realities, presumably on behalf of the wealthy elites still trying to push the message that “hard work and good hearts still win the day”, rather than being horribly crushed by big business folks and the politicians who work for them.
(Your gong-fu may be strong, Jimmy. Goldman-Sachs will still pwn you.)
Thus, by being an older film, in black and white, and calling to mind a more innocent era of the American dream, viewers tend to distance the film from more direct analysis, or “what ifs”, and simply enjoy the nostalgic Christmas-y goodness.
(Nothing, however, can change the fact that your daughter’s name is Zuzu.)
This answer originally appeared on Quora: Why isn’t the film “It’s a Wonderful Life” seen as being more depressing than it is?