I really dislike the thought of running epic months-/years-long campaigns. In theory, it sounds like it could be interesting, but then it just breaks down under real world conditions. You’ll rarely find a solid group of consistent players and if you’ve already worked it out that its going to take months to get through, you’ve kind of already decided to start railroading the players (though you can allow for improvisation, the overall story’s structure is pre-written).

I much prefer running one-shot adventures, maybe lasting <10 sessions at most, where I have as little idea what’s going to happen as the players and there’s no pressure to keep things going. It just lets me work on the general feel and concept for the game I want to run and not worry about funneling the players through a set of specific story beats or work out what’s happening in the background amongst different factions, etc. If the players liked running improv, just go with it then, true improv in gaming feels so rare (at least in my gaming group I think).