Assuming what we’ve got now is the first “Act” and it lasts about 15hrs on average to complete. Multiply that by 4 and the base game would have around 60hrs completion time for the campaign alone which is awesome.
Add side quests, end game activities, and what not and we could see it go well beyond 100hrs.
I think this game has a huge potential and the devs should capitalize on its “aRPG” aspects to extend its longetivity, which is mainly about replayability concerning things like builds, randomization/RNG, and procedural generation.