If it really is 20 hours, it's quite perfect for me, especially if the pacing is great. As a grown up with a career that requires a lot from me and a personal life, I can't do 100 hour RPGs any longer, except the odd occasion like Dragon Age Inquisition (200 hours) because I love the world/lore, even though it was still a disappointment when compared to Origins. Dropped The Witcher 3 after 30 hours.
For a RPG I'd say anywhere between 20 to 30 at most is ideal. Any more than that and you get padded pacing, unneeded grinding and a high risk that players will lose interest and disconnect.