BBC says the film
achieves a fine balancing act between pathos and feel-good that is delivered by an outstanding cast.
Roger Ebert says, "What is remarkable about "It's a Wonderful Life" is how well it holds up over the years," and that it is "not just a heart-warming "message picture.""
I agree more with the New York Times review as it states
the weakness of this picture, from this reviewer's point of view, is the sentimentality of it—its illusory concept of life. Mr. Capra's nice people are charming, his small town is a quite beguiling place and his pattern for solving problems is most optimistic and facile. But somehow they all resemble theatrical attitudes rather than average realities.
The New York Times says the film is
a terrifying, asphyxiating story about growing up and relinquishing your dreams, of seeing your father driven to the grave before his time, of living among bitter, small-minded people. It is a story of being trapped, of compromising, of watching others move ahead and away, of becoming so filled with rage that you verbally abuse your children, their teacher and your oppressively perfect wife. (HT: GreenCineDaily)I agree wholeheartedly with that reviewer.
Here's the lost ending, introduced by William Shatner: