It pretty well depend on the game.
I would say my current situation is that i didn't play much solo stuff in years and i want to catch up. I have A list, B list and C list of games already released since long or recently released, of early access, or not even released that i want to play, and i would much prefer not having to sink 200 hours into it, like Fallout: New Vegas. About games being sorta good, not being played, i would say that it would be kinda hard as, IMO, no game is perfect. There is always something to complain about it.
I picked 20h-30h personnally, but it isn't a rule. I enjoyed some games that could be finished in 10h-15h, like SR DMS or Remember Me. I was also very disapointed by games being shorter than 10h, DLC included.
On the other hand, some games that are longer than 30 hours, could be just gold. I don't know exactly how long The Witcher was, but the fact there is so many plots, so many characters to interact with, so few fillers, and that is was splitted in chapter, made the experience quite great. I didn't feel i was overwelmed by unecessary filler contents, which matter the most.
But even if the game is great 100 hours feel like overkill to me. When i see written that game X has more than 100 hours of content, it feels like a factor for NOT getting the game.