We just finished up my campaign, a little over 16 years from when we started it back in '92. It spanned three editions, but the characters progressed steadily and finished up at about lvl 23-24. It was the right time to stop - both story-wise and because the math was getting onerous - but our last game was great, with several PCs giving their life to save everything they held dear and other PCs getting to live because of their sacrifice.
When it was over, we just sort of sat there for a few minutes. Feels weird. I think we'll hold one more session where we have dinner and everyone can ask me any question they can think of.