Pet Semetary was a really bad movie mostly due to terrible acting, but it's a really good story and maybe Stephen King's first real psychological horror story as opposed to physical horror. Basically, if you could bring a loved one back from the dead but they would not be the version of them that you remember, would you do it? 1980's filmmaking tended not to be very good at subtlety and introspective thought.
The League of Extraordinary Gentleman was another terrible movie as it tried to be a typical comic book movie from the era it was made. I know it was a comic and I haven't read it, but you could tell that the characters were supposed to have depth and individual storylines. The characters were all ripped from historical fiction, ie Captain Nemo, Tom Sawyer, Dr. Jekyll but none of them seemed to be playing those characters straight, or as they would be from their original source material. It was just mindless action with no depth but it is a clever idea that should have been good.
There was a really terrible Adam Sandler move called That's my Boy. He played a guy who as a schoolboy had a relationship with his teacher and they had a kid. The movie made jokes about and showed the impact of the incident to Sandler's character, his parents, his teacher and of course the kid as an adult. It also showed how Sandler's character had been a pseudo celebrity due to the incident. The movie was a terrible, terrible and offensively unfunny comedy. But I think it would make a really good story from a dramatic standpoint, particularly the becoming a 15-minutes-of fame child celebrity due to being the victim of something notorious and horrific that you'd never be able to separate yourself from.
That Will Smith movie Hancock was a dumb superhero movie but it was REALLY supposed to be about how terrible a superhero's life would be due to alternating between being a celebrity hero and being reviled because your super powers cause so much destruction. I think having a straight story like that, without antagonists and big battles would have been interesting, though I think the horse has already left the barn on that one since both Marvel and DC have now recently addressed both of those ideas, even if rather sloppily.
The movie Hair was also terrible, and while I don't know that it needs a remake (from the play) the timing of that movie is just bizarre. It was made in 1979 which was much too late to be relevant to the counter-culture movement and waaaaaay too early for that time period to be retro and interesting again.
And of course The Godfather Part III.