I don't think he means that there is anything wrong for Stardew Valley, a game, to not be "rewarding" (and thereby rewarding here is defined as something beyond

I don't think he means that there is anything wrong for Stardew Valley, a game, to not be "rewarding" (and thereby rewarding here is defined as something beyond entertaining). But if Duolingo as a learning tool is like that too.. that's a problem.