Ico - It's around 5-6 hours, and is a game everyone should experience at least once as even with how vastly influential it is, there still isn't quite any other game that captures it's unique vibes other than The Last Guardian at times (TLG almost qualifies itself for this thread, and can be beat in under ten hours but average is higher)
Brothers : A Tale of Two Sons : By the same director as TGA GOTY winning It Takes Two, this is still his magnum opus, and has the single most impactful moment of gameplay-story integration I've come across in my over two decades of gaming.
To The Moon : There is not much gameplay here, but it's story is incredibly well told and heart-wrenching.