Saw it a long time ago and wasn't particularly impressed with it as I recall.
It was made at the time in movie-making when Irwin Allen's output was flavour of the month, so it's very much in the style of lots of mediocre mid-to-late seventies disaster pictures, i.e. Airport 75, 76, 77 etc and The Towering Inferno, none of which are exactly what you'd call classics.
Hollywood does this kind of thing all the time. One year its meteorites heading towards Earth, the next year it's action adventures on mountains...
Most films of this ilk have a huge budget, several big name stars and a predictable storyline. To be fair Gray Lady Down is not the worst disaster picture ever made, but certainly not one of the best either.
Chock