I've had a lot of multi-year campaigns over the past 30+ years so it's hard to pick out one. I've noticed that for the last 15 years or so that my campaigns (the ones I run anyway) tend to go one of two directions: Either they run six sessions or less, or they will run for more than a year and last 20+ sessions. Some of those short ones are deliberate one-shots or limited campaigns, and some of them , well, we just figure out it's not working for us right now and change things up.
- Once I settled in Texas our AD&D games were all played with the same group of characters over a period of about 8 years and could be considered one long, loose, campaign.
- Our AD&D Second Edition games were mostly centered around one long Forgotten Realms campaign that ran on and off for another 8-10 years. There was even a "next generation" continuation of it during 3rd edition.
- I was part of a Twilight 2000 campaign that ran for about 3 years and covered the voyage from post-nuclear Poland back across Europe, the Atlantic, and back to the U.S. I'd love to try that for a new group of players today.
- I also ran a Rifts campaign for over a year. It can be done!
- I ran a 4th edition campaign that went about 30 sessions over a couple of years - Return to the Ruins of Adventure
- I then ran another 4th edition campaign that went about the same distance - Savage Swords of Impiltur
- Right now Wrath of the Righteous has been running for almost 2 years and about 30 sessions (with several significant breaks) and if we finish it I suspect it will be the longest game I've run in a long time.
So I've settled into a mix of short games in and around one long term campaign and that seems to work well for us. Hopefully that continues.