Luckily, we had the chance to eat at Didi's Frieden before most of Zurich's restaurants closed for the Christmas holiday. Didi's has a warm and festive atmosphere that you would not gather from looking at online photos. We did not have dinner reservations and the restaurant was full, but they were able to accommodate us at the bar... Which ended up being a lot of fun, as they have great wines by the glass, and an enthusiastic bartender who provided excellent recommendations for pairings and generous tastings. We ordered two of the day's specials: a warm seafood salad with an avocado dressing and thinly sliced duck carpaccio served with foie gras (words can not do do either of these justice), vegetable crepes, and as entree with we had the sea bass with fennel. For dessert, we had the passion fruit creme brulee and chocolate tart. Even at the bar, Didi's is great place to linger and enjoy a meal.
Rive Gauche at the Baur au Lac is one of those restaurant/lounges that irritatingly oversells you... In particular be conscious of the amount of water bottles that they bring to the table - at the end of the meal we had 3 unfinished bottles of water and paid $80 US dollars for water. What I can heartily recommend here is the "Quacks and Pickles", and the "Be Bullish" with the country fries (to dip in the gratin sauce, yum). All the other dishes were okay. Better than most "hotel" restaurants, and does seem to draw locals.
Christmas brunch at Baur au Lac was a decadent affair. There was a cold bar which served salads, pates, salmon, etc... and a warm bar that encompassed most traditional Christmas fare (moistest turkey I ever had, roast beef, potatoes anyway you can imagine, vegatables, etc...), and a multitude of desserts (cakes, cookies, puddings, creme brulee, chocolate mousse, tiramisu, etc...). It was definitely the best brunch that I have ever had.
For Christmas dinner, Kronenhalle was one of the few restaurants open. Given past reviews, my expectations were low. However, I was pleasantly surprised. Normally, I tend to go for the specials of the day, but usually with this the type of restaurant I find it best to stick with the classics. Those of us who ordered off the traditional menu enjoyed our meal (roasted baby chicken, veal cutlets, and sliced calf liver), whereas those who ordered from the daily specials were disappointed (so much so, that cannot recall what they ordered!). Kronenhalle has a warm, convivial atmosphere that is conducive to having dinner with the family or an old friend. I imagine that is a large part of its draw... Oh, and the Chagall's.