We enjoyed a wonderful 3-night stay at Windermere House. Gorgeous setting, of course, on the shore of Lake Rosseau. Very nice, well-appointed room. Great recreational offerings, all included (we availed ourselves of the swimming pool and hot tub, and took a pair of kayaks out for lovely paddle). Unusually friendly and attentive staff. Better than average complimentary breakfast buffet.
Our only complaint was about the dining options. There are 2 venues: the high-end The Rosseau and the more casual Windermere Pub. Both offer beautiful indoor and outdoor settings; but both are very high-priced and offer a lot of dishes with excessively fancy ingredient lists, which offer more show than substance. Some dishes under-deliver, e.g., the pasta with "mushrooms": our servings each included a single halved mushroom. Vegetarian options are very few, vegan ones fewer. It was very difficult to find healthy food options.