Oh, I completely agree that plotwise the movie suffered. I remember commenting how weak it was compared to Jaws, E.T, Close Encounters and others. Spielberg was so busy with all the technical aspects of the project, and the writing suffered.
It was also a mistake to take the most interesting character out of the movie 1/2 way through, Golblums "Dr. Malcolm".
Sam Neal is a bore in everything I've seen him in, and compared to her performance in "Wild at Heart", Dern was no big addition to an otherwise great cast.
Like King Kong, the true stars of the movie were the technical wizards that created the creatures, set design and musical score.