Walking into Ranzen is like walking into a retreat. I find it instantly calming. I have always enjoyed the food, especially the most traditional dishes, the soups and the vegetarian dishes. Now that there are several other Tibetan restaurants in the area, I find that Ranzen has some strong competition in the areas of food and service (so slow!), but no restaurant around matches Rangzen's atmosphere.
Just fyi, I always have the urge to go to Rangzen on Sundays and Mondays, and I think they are closed both days. Call to check before making the trek.