You laugh, but I thought Speed was a pretty good movie for as long as the bus was running. It was oddly compelling. There is something to be said for momentum in storytelling. You can bridge amazingly large gaps of logic if you just keep the plot moving.
Before the bus is running the movie is completely unmemorable, and after the bus stops running the movie falls apart and starts to suck. Which is pretty ironic.
Producer: If the bus stops, it blows up.
Movie Exec: That's it? The "Hey Verne Guy" movies had better plots than that! What the he...
Producer: We've got Keanu all set to star if we get sign off.
Movie Exec: OH! Why didn't you say so. I bet we can get 50mil for production.
Producer: Make it 60 and you're on.