I went to the Water Grill Oyster Bar recently and I was very pleasantly surprised by the quality of the food. The specialty of the house (besides raw oysters) is a very tasty gumbo. I'm not sure if it's the best in Tokyo, but it was quite good - rich and thick, spicy enough for my taste, with plenty of lobster and crabmeat. I had the standard white-rice version, but it also comes with okoge (crisp, Japanese-style toasted rice cakes) or Asian noodles, which might be a bit gimicky, but maybe worth a try anyway. (There are only two or three other places that serve gumbo in Tokyo, so it's a welcome addition for that reason alone. And there's only one other oyster bar that I know of.)
Besides the gumbo the only other main dish I noticed was the fish of the day, but there are a lot of hot and cold appetizers, soups, cooked oyster dishes and of course raw oysters. My favorite dish was the fresh sea urchin omelette with truffle and sour cream sauce, a well balanced succession of delicate flavors without any one of them overwhelming the whole. I also enjoyed a nice foie gras and chopped shrimp in pie crust, and something called Water Grill Caesar Salad - not really a salad at all, but an interesting combination of ingredients (avocado, Parma ham, ricotta cheese, and some greens) wrapped in a tortilla. In short, there's plenty of great food even if you don't eat oysters (which one of my party didn't).
The wine list starts at around Y4000; we had a spicy Yalumba Shiraz that stood up very well to the gumbo. Oddly for an oyster bar they only had one variety of oyster when we were there, but they did warn us when we arrived (late on a Saturday) that they were running low on the oysters. They boast on their website about serving various types of oysters from different parts of Japan, although I would think that they'd serve New Zealand oysters in summer. The raw oysters come with five different sauces, including Korean miso-based, spicy Cajun style, lemon juice, soy sauce-based, etc. We had plump, very fresh and tasty oysters from Miyagi Prefecture, Y390 apiece.
The room itself is comfortable and stylish, done up in a white color scheme with lots of white curtains, white glass-topped tables and an open kitchen area. There's seating for maybe 20 at the tables (along one long curving white leather banquette) and another 10-12 at the counter (also white). It's located in Akasaka Tokyu Plaza (right above Akasaka Mitsuke station); the entrance is on the second floor (all the way at the end towards the highway), but the dining room itself is up on the third or fourth floor. Dinner is around Y7000-10,000 per person with drinks.
Water Grill Oyster Bar. 3539-1700. Open 11:30am-2:30, 6-10:30pm (LO). Closed Sundays.