There may be newer ryokans in Kurokawa or ryokans with more picturesque onsen baths but for sheer rustic charm, nothing beats Shinmei-Kan. Its cave onsen is certainly unique but it is small and can be cramped. The entrance to it can also be slippery and daunting, not to mention it lacks privacy. Its indoor baths are basic and not inviting. Its private baths could do with a more pleasing aesthetic makeover. So too could the lobby of the ryokan itself which is also rather basic - I guess that was the intent so as to preserve its old-feel charm.
In terms of its location, it commands the Center of town and is unmissable by anyone who passes it. Its fairy tale allure defines the town itself and it is not unusual to suppose every visitor to Kurosawa taking a picture of it posing on the bridge to its entrance. The downside of all this attention is the compromise on privacy and intimacy offered by its rivals.
However it lacks nothing when it comes to its hospitality. The staff are first rate, and so too are the meals.