IMDB's top 250 list comes directly from users' ratings of the films on their website. The more popular the movie is, the more hits it receives, the more ratings it will most likely receive, in turn gives it the momentum it needs to travel up the rankings to make that top list.
It's based entirely on their point scale & number of votes.
So what happens is as new movies are being released, or coming out on dvd people are reading about them online, and viewing them & then voting on them while they are still current.
Most of your older movies just as good or better than recent titles have been overlooked as they are not generating as many new hits on the site, and not nearly as many votes.
I will say this much, Shawshank Redemption is one of my favorite movies of all time! I don't know how you can compare alot of the movies across the various genres & especially across so many years of film, but Shawshank would be in my personal top 10. I'm not sure what number order I'd place on any of them, but it's be in the top 10 for sure.
Green Mile is very good as well, but Shawshank had a more realistic storyline. It's a simple, believable story about a guy who's been wrongfully accused & how he's able to overcome this hand he's dealt. There are no super powers at work, and nothing out of the ordinary. The warden & staff play such evil men that you really hope for the best & that justice will prevail in the end. So maybe it
is a happy story, but it's one that I enjoy very much, and one I would place very high on any list of top 100 movies.
Another good prison movie I like is Dead Man Walking. This one, written & directed by Tim Robbins, takes a different angle on good vs bad. The bad guy ultimately gets what he deserves in the end, but you're left feeling sorry for him in the process. I thought it was very moving. Sean Penn plays alot crybaby roles! I like him alot in 21 Grams too.