IAWL is a good movie, but not a "masterpiece" and in terms of how much it's overplayed and built up as the greatest Xmas film (it is NOT a Xmas film, it is primarily a biography!), it is overrated.
Beloved of "film buffs" probably tells me all I need to know. ;-) As a child in the '70s I never once had even heard of it, and I watched old movies alot on plain TV (no VCRs in those days, you know). Apparently the film buffs didn't get their way until the late '80s.
Again, it IS a very nice film and 1 I like to watch, but it's just overrated (<- means "rated higher than it should be", not "bad").
XMAS movies are defined pretty vaugely. Any movie with a Christmas scene in it apparently. By masterpiece I was reffering to issues of cinematic texture and nuance. Capra's mise-en-scene had never been so fluid nor had his direction of actors been so natural. The scenes with Jimmy Stewart courting Donna Reed almost seem improvised which was a highly unusual acting style in those days. By comparison, 'Miracle on 34th Street' is not very cinematic and is more of a filmed play. Enjoyable but not great cinema.