re: Movies with really good ideas as the basis, that didn't work in reality

In Time is my go-to for this. Such a cool concept, but then they hired Timberlake and Seyfried, and both sucked massively.

Jeepers Creepers could possibly qualify. Loved the concept, and the first half is amazing, and then it just becomes hilariously bad.

The Core could also work. I thought the concept was cool, and I actually kinda liked it. But most people hate it and think it's pretty horrible. And upon rewatch it really does have a ton of flaws and although it was a cool concept, it didn't really work too well.

I want to say Sunshine, because that was a cool arse idea for a movie that ended up failing to deliver on all of its awesomeness in the third act...but I feel like that may be just the creators of the movie fricking up rather than the movie "not working in reality." (ETA: and I still love Sunshine)