The thing is, "Airplane" was the first of it's kind, really sort of ground-breaking, and personally, I think it's the best. The problem was that they kept on doing them (and the Naked Gun movies), and while the first one was incredibly funny, they really were stretching for material on the sequels.
But I still think "Airplane" was a classic, and today I'll still watch it, mostly because I can repeat all the lines of dialog.
Mark
There is a movie from the 1950s with Linda Darnell and Dana Andrews, from which the movie Airplane derived much of its plot. The original movie, Zero Hour, was a serious movie, but when you watch it after watching Airplane, it is hilarious. The ground crew head guy even said, “I picked a bad time to quit smoking.” I caught it on TCM sometime last year, and wish it would come on again.