This is a traditional, older style onsen in a great location.
The positives are as follow:
1)the outdoor hot spring is the main attraction. For 5 minutes, I had the hot spring to myself!
2) dinner is very good, specifically the selection of sashimi, amazing
3) the view of the lake
The negatives are as follow for August
1)The room is basic, no AC, and shower. The fan helps but they provides a heavy blanket not appropriate for the weather, season
2) buggy, it was hot so the fresh cool breeze at night from the lake was great, but the window screens are not sufficient to prevent flying insects. The screens and the windows have gaps. We spent the night killing bugs on the tatami.
3) hotel is dated holding on to the tradition
There are better options around the lake.