I think one shots can be fun, and at a convention are a good way to play a game when you might not have been able to do. But, I also feel most games become more interesting the more time you invest with them. The choices you make each session become more meaningful. You end up caring about the characters more. With a lot of OSR games people start of playing generic adventure person that will slowly evolve through sessions into an actual character. I think campaign play is often the most compelling aspect of an RPG. And the RPG games I look back on most fondly have all been parts of longer campaigns.
Trying to make games that work as compelling one shots seems like a good goal, because people often don’t have the time to play a long campaign. A lot of D&D adventure I have seen in recent years seem built with the idea you could play them in a convention sized slot. (Basically everything from DCCRPG for example.) Many indie games seem built this way as well. I think games that purposefully try and come to a nest conclusion work better here. Otherwise you just leave wanting more. Maybe not the worst way to feel after a game, though.