Like many Americans, I saw the remake "Birdcage" first. Only recently did I get a copy of the original. "La Cage aux Folles" is a great comedy, well deserving of its praise and classic status; I just wish I had seen it before I saw "Birdcage".
The reason is (through no fault of the original French filmmakers and actors), the American remake is one of the few films that did a good job of suiting it for American audiences. They got some of the most recognizable and endearing actors, and they really played on the humor of America's brutal division between Conservatives and Liberals. In other words, it hits home.
"La Cage" carries more of a nostalgic distance, in the fact that it's both European and an older 70s film. Like watching "Casablanca", you can get engrossed in the film, but you never quite picture yourself in context ...especially when you keep thinking of Robin Williams and Nathan Lane who both did an excellent job of staying true to the original characters played by Tognazzi and Serrault.
OK, enough irrelevant comparisons. I just wanted to get that out first, in case you're pondering whether to watch "La Cage" or "Birdcage" first. Definitely start with "La Cage".
"La Cage aux Folles" is simply fabulous. With a screenplay by Francis Veber, whose pinpoint comedy and wit makes him a modern day Moliere, you can't go wrong. Gags are handled with the perfect finesse, even the corny slapstick ones. The scene where Michel Serrault is learning (very unsuccessfully) how to butter his toast "like a real man" had me howling. I can't imagine how Ugo Tognazzi could keep a straight face.
Other memorable gags happen throughout the film, and whether you're French, American or Martian, you've got to understand the universal language of comedy. Serrault's high pitched yelp gets my vote for funniest and most infectious sound uttered by a human since Homer Simpson's "D'OH!" The story itself, while purportedly being about drag queens of loose moral character (haha), is safe, clean and absolutely fun for the whole family. Sexuality aside, it's simply a classic comedy of errors that anyone can enjoy.