They have an amazing selection of teas and tisanes (something like 200 total), for either brewing in or buying and taking home. My spouse meets a bunch of knitters there once a week, and I tag along to get a good pot of tea and a nice tea sandwich. They also have a good selection of pastries on hand, that varies with the time of day and the desire of the operators.
It's particularly nice in the winter, go in, get a pot of warm tea, watch the rotten drizzle outside while you're warm, drinking tea, and eating a smoked salmon tea sandwich.
It's not a restaurant, per se, it's a tea house more in the proper sense. Tea, not coffee.