Thing about Isawa Onsen is that, yes it's a flat, non-descript, residential type of setting. But once you check in, people generally stay within the ryokan until check-out. So what makes or breaks for me is the ryokan itself, although the surrounding is not completely unimportant. And there's a few really good places in Isawa. There's a range of ryokans in terms of quality. There's even variation in the quality of onsen water from one place to another. Keizan is my favorite. Great views of Southern Alps if your room is on the right side. Good dinner, fabulous breakfast buffet, nice onsen, nice room, real konbini in the lobby. But, for me, the ultimate onsens are up in central Alps.