On my first viewing I had the same response. I've decided that the movie is a story about how innocence defeats evil. At the end, Potter, a dishonest thief who's made a lucrative living at it, has an extra $8k; George Bailey is surrounded in his own home by everyone who loves him, people who owe their lives to him, a great big Christmas tree, no fewer than two government officials publicly acquitting him, a 4-bushel basket of cash- $20s and $50s floating in the air - a free piano player, and wine.
Potter's already in jail, has been the whole time. George has always been free. Nothing can ever keep him down for long.