We stayed in Tokinoniwa for 1 night and stayed in the in-room onsen with the 40.28m2 room.
Location: a bit far from the main onsen village, which is fine for us since they offer free shuttle from hotel to main onsen village with early and late night, so no need to worry that you can't get to the village
Room standard: we stayed in their biggest room which is nice, however, the room inside is actually a bit older than I expect, and since their entrance and lobby are so well furnished and looks new, so that I expected the room will be the same; however, it is not, so it is a bit disappointed...
EXCELLENT free bus shuttle to Karuizawa - make sure you book it in advance, I believe this is such a GOOD nice service that they have. It saved you many transit and train changing time.
Staff: all staff are wonderful, their service is one of the best
Dinner - We sat in a private room from their restaurant floor. I had onsen meal many times, but unfortunately, I would said their dinner is one of the not-so-good onsen dinner that I ever had, they started with many starchy food, and their the seafood grill's seafood is not as fresh, and the sashimi we found a piece fish scale when we ate (which I believe this is a big no-no for onsen/japanese meal), and the sukiyaki seems only sweet, we don't taste much for the soup stock (konbu or any other taste). Therefore, we were not so satisfied for the dinner.
Breakfast - we got sat in the restaurant floor but not in private room this time, it was much much much better than dinner, or i have adjusted our standard for their food, anyway, the breakfast was good, we both choose the JPN style, grill fish and congee/rice, it was way better and the taste for the pickles/veggi have reach the standard
In conclusion, we think this is an OK stay, we spent around USD$500 (2 people for night, 2 meal), honestly, I would exepect expect a bit better experience. I will say the bus service and many outdoor onsen to try are the highlight of the hotel.