I liked Underwater for what it was.
The final monster was straight up Cthullu though.
For my part, I watched Altman and Feifer's adaption of E. C. Segar's POPEYE comic strip with Robin Williams, Shelly Duvall, Paul Smith, Ray Walston, etc. Its the 40th anniversary of the films premiere, in December 1980. Its long been a favorite film. Possibly one of the best odd-ball films ever made. It still amazes me that the studio so hated working with Altman that they played up it being a failure (despite making 3 times its budget in the initial box office run).