You summed up my opinon on it as well. Was really enjoying the film, it got to the end and I though, great! Except, that wasn't the end. Suddenly we go into a sickeningly sentimental crap alien movie.

The 'death' below the sea was where the movie should have ended. i suspect in Kubrik's original draft it -did- end there. But the idea of leaving the film with a downbeat ending probably offended Spielberg.