Williamsburg is a decent neighborhood for food: lots of above-average spots, but only a few really outstanding places. It's good to have a nice variety within walking/ordering distance, but for some cuisines (see starred categories), you'll really need to venture elsewhere to find superior food.
Asian*: Sensation (Chinese), Sea (Thai), nha toi (Vietnamese), Bistro Petit (Korean-ish), Dokebi (Korean BBQ), Taj (Indian)
Australian: Five Leaves
Barbecue: Fette Sau
Contemporary / New American: Marlow & Sons
Deli (Italian): Graham Ave. Deli
French: Le Barricou
Gastropub: St. Anselm
Japanese*: 1 or 8 (Sushi), Ramen Yebisu (Ramen), Zenkichi (Izakaya), Samurai Mama (Udon)
Mexican: Mesa Coyoacan (upscale), Mexico 2000
Modernist: Gwynnett St.
Middle Eastern*: Cafe Mogador (Moroccan), Zizi Limona
Pizza*: Forcella (Neapolitan), Williamsburg Pizza (New York)
Seafood: Maison Premiere
South American: El Almacen (Argentinean), Tabare (Uruguayan), Chimu (Peruvian), Caracas (Venezuelan)
Southern: Pies n Thighs
Steak: Peter Luger's
Tasting Menu: Aska
Cliffs Notes: If i had to pick 5 must-try's from the above list, they'd be, in no particular order:
2. Gwynnett St.
3. Maison Premiere
4. Peter Luger's
5. Fette Sau