Ok, I prefer Holiday Inn to White Christmas, but to label WC not good is a bit harsh.
The chemistry between Bing and Kaye was sharp, Rosemary Clooney was never more beautiful, the color was lush, the heart-warming tribute to "the old man," the confusion over Bing's motive, the cute Snow number on the dining car with the napkin and parsley, the snowfall at the end of the film, Bing and the rest of the cast in Santa suits... heck, I want to pop the movie in my player right now.
It's probably not in my Christmas film top 10, but to say it's not good, is bit overboard even for one playing devil's advocate.
As for the thin plot, well, fine, but every movie doesn't need to be The God Father, particularly musicals. No doubt it was pieced together as a vehicle for Bing singing Berlin, but to me that combination alone is reason enough for a movie.
And there is romantic conflict when Clooney misunderstands Bing's motive.
I quite enjoy the military opening - which had to have influenced Robert Altman's MASH - and there really is no way to convey how much The title song meant to the servicemen during WWII.
Well, I've rambled enough. The film is a Christmas classic in terms of popularity and that makes it GOOD to me.