Asklemmy

The Cube.
Most people saw it as an average horror movie where a bunch of people try to get out of a giant torture box. But there was a pivotal scene that stuck with me where one of the prisoners realizes he helped build part of it. The whole thing wasn't some intentional torture device but just a bunch of people doing their day jobs that were lost in a bureaucracy not ever questioning what their work was creating.
A stark reflection of society and the systems we create and the dangers of not ever looking at the bigger picture.

Of course they proceeded to shit all over this idea in Cube2 where it ended up being just another evil government experiment.

I feel like the last 30 years of Star Wars movies could qualify here

The movie In Time (2011). The premise was interesting but I can't even remember the plot because it was so meh.

I also think Idiocracy could have been better. It had good moments, and that's what most people remember, but the overall cohesiveness falls flat. Great moments, iconic scenes, but could have been a better film.

Not a film, but a TV series? It's called Jericho, and the synopsis in the Wikipedia reads:

Jericho is an American post-apocalyptic action drama television series, which centers on the residents of the fictional city of Jericho, Kansas, in the aftermath of a nuclear attack on 23 major cities in the contiguous United States.

But yeah, the execution is mediocre at best. Both the action and the drama are unbearably flimsy and cliche, even the argument flops as metal.

Twilight. My wife made me watch the first one and it's actually got a really interesting world and hints at a lot of decent lore and possible content.

Then they fill the film with close-ups of their eyes meeting across the room for minutes on end.

There was this movie I saw once called Time Trap. I definitely would not call it good, but the premise was interesting.

Archaeology professor goes missing while exploring a cave which was once thought to be the location of the fountain of youth. His grad students go looking for him, find the cave, weird things start happening when they enter.

Not a movie, but a TV Show. The Cape.

A former detective is forced into hiding where he is trained in stage magic, sleight of hand, circuscraft, and illusions. He uses them to fight crime.

I thought it was a really interesting concept, a more down-to-earth superhero like Batman, and stuff like this can plausibly happen in real life.

Unfortunately the show was so bad it was canceled mid season and the finale was only streamed on NBC's website.

Quite a few MST3K films have a decent premise IMO, but lacked either the budget or the talent to make enough of them.

Eg Time Chasers (which isn't really all that bad), The Skydivers, Moon Zero Two, Rocket Attack USA, Stranded in Space, and perhaps even Manos: The Hands of Fate.

With the right people, I think those and others could have been very decent movies.