The plots, of course, are basically the same. Socialite Tracy Lord (Grace Kelly), despite men espousing the opinion she's an ice queen, is about to be married for the second time. Her ex-husband (Bing Crosby) may or may not be aiming to stop the nuptials. To complicate matters further, the family is blackmailed into allowing a journalist (Frank Sinatra) to report on the social event of the Newport season. Said journalist may or may not develop a bit of a crush. Three men; one lady- the math proves there will be just enough chaos and confusion to fill a film.
The biggest difference between the two films is that High Society is a musical. This should be of no surprise. In addition to crooners Bing Crosby and Frank Sinatra, Louis Armstrong plays himself, functioning as a sort of musical narrator talking and singing directly to the audience. In fact, it was Cole Porter's first original film score in eight years, and it produced several modest hits and a lot of forgettable tunes. If nothing else though, it gives viewers marvelously funny (if narratively unnecessary) duets between both Crosby and Sinatra; and Crosby and Armstrong.
So what else changes? Both the original Philadelphia Story and its remake are set in their own contemporary times- the 30s and 50s respectively. High Society does relocate itself to Newport, a land of Vanderbilt mansions. Perhaps it is the change of decades that induces this, but High Society has some rather baffling commentary on the decay of the upper classes (in ways reminiscent of the film Sabrina), while at the same time seeming to express that those who worked for their money are to be looked down on. The script did this by not only making the self-made man Tracy is about to wed a bit of a controlling prig, but it also softened the first husband's faults. When Cary Gran played the role, it was a recovering alcoholic; Bing Crosby in the role is given no such character flaw, and so the reason behind the divorce is never entirely clear. The story also gives more time to build the backstory between Tracy and her first husband, making him a more viable romantic interest.
The real differences through show in the casting. Elizabeth Taylor was originally wanted to play the lead and when she was unavailable, they went the blonde root. Grace Kelly may be one of the most beautiful women to look at (and is even more so in all the film's frothy gowns . Her costumes for this were a wedding present from MGM on the occasion of her marriage to the Prince of Monaco). But, as the New York Times review said,"... with pretty and lady-like Grace Kelly flouncing lightly through its tomboyish Hepburn role, it misses the snap and the crackle that its un-musical predecessor had." Grace Kelly does sing through, the only time in her career that she did so, and she reveals a lovely voice in the process. Bing Crosby, who always plays himself, sort of mozies from place to place while on screen, never seeming worried about his ex getting remarried or particularly awake even, let alone impassioned. Though the plot made it more believable that Tracy Lord would consider getting back together with this man, it doesn't help their chemistry that Crosby could have been Kelly's father, being nearly twice her age! Sinatra has a fun romp about as the reporter, but he faces the same issue Grace Kelly did when she stepped into Katherine Hepburn's part. It is just always going to be hard to live up to Jimmy Stewart.
Funnily enough, since it was, even at its inception, rather famously a remake, the film was nominated for "Best Writing- Original Story." It turns out the Academy confused the film with one that had been produced the year before under the same name! The nomination was gracefully declined when the mistake was discovered.
All in all, High Society is no Philadelphia Story, but if you are looking for fluffy entertainment in the form of pretty dresses, and a few good song and dance numbers all filmed in Cinescope, it is worth the watch. You can pretend that you too are a part of High Society.