As another reviewer said, the Ultimate title is slightly exaggerated, but it isn't far off! The most important omissions are the Undersea World which is available separately and is merely two discs short of this set so it is fair to say it was rightly considered suitable for it's own release, as are the three bona-fide movies, also available as a set.
This set includes all the later stand-alone episodes and TV series:
Oasis In Space (1977)
The Cousteau Odyssey (1977-1982)
Amazon (1982-1984)
Mississippi (1985)
Jacques Cousteau: The First 75 Years (1986)
Riders Of The Wind (1986)
Rediscovery Of The World I (1986-1989)
Island Of Peace (1988)
Liliput In Antarctica (1990)
Outrage At Valdez (1990)
Rediscovery Of The World II (1992-1994) but see note below
Madagascar (1995)
My First Eighty-Five Years (1995)
Diamonds Of The Desert (1996
Sanctuaries For Life (1996)
Across China With the Yellow River (1996)
Lake Baikal (1997)
So, apart from these, what is actually missing?
Indeed, the only ommissions are 1982's Cries From The Deep (Les pièges de la mer, Jacques Gagné), the stand-alone episode Saint Lawrence: Stairway To The Sea, and curiously, one episode of the Rediscovery Of The World II called The Mirage Of The Sea, which must surely be an oversight as the other twelve are included here.
Also, his short documentaries from 1942 through 1956 are not included, but it is hard to find much information about these and I suspect they would be in French and b/w. Who knows?