I like the way KotC2 handles this with modules. This way you get multiple different games using the same engine. You can put many hours into it while keeping each game dense with interesting stuff.
Yeah, I love playing modules or maps for my favorite games. I'll play everything that comes out for KotC, and my most-played game ever is Thief because of its many fan missions.
The problem with games that are very long is that they usually don't have enough unique content to make all of these hours interesting. And the difficulty curve gets wonky at some point, in RPGs you gain experience and the game should in some way be balanced to have an engaging leveling curve where it stays challenging but fair throughout. Overly long RPGs tend to have the player become overpowered long before the game's end, especially if there's a lot of optional sidequests and you approach the game as a completionist, doing everything there is to do before you head on with the main quest. In shorter games that's less of a problem.
So having a set of 10 modules, each of which takes 10 hours, has challenging hand-made encounters, a bunch of side quests, and choice and consequence with multiple endings, is better than having one 100 hour module that follows the same design principles but is overly long.