The best restaurant in Olney is Le Mannequin Pis, a Belgian bistro that's a little hard to find on Georgia Ave but worth the effort. From there, the bar drops far, quickly. BJ Pumpernickels is a decent approximation of a NY deli.
Olney Ale House is nearby, but I do not recommend it. Mama Lucia is also there, but I find all of the locations except for Rockville Federal Plaza to be wanting.
Mannequin Pis Restaurant
18064 Georgia Ave, Olney, MD 20832
le Manenequin Pis: outstanding Belgian Bistro with 15 ways to cook a kilo of mussels, great but expensive imported beers, nice wine, gourmet menu
Bella Notte: Average family Italian
Riccuitti's Wood Burning Stove: grown up gourmet pizza's, pork chop. crab cake, the best desert pizza in old antique national landmarked house
Pumpernickles: NY style deli: corned beef, pastrami, brisket, chicken matzoh ball soup etc
Sospiro's: new rustic Italian food and wine bar, no veal parmisean on this menu, try the pasta with veal ragout
Mama Lucia's: Family Italian and good NY style pizza
Cheeburger/Cheeburger: burgers and shakes
Hunan Delight; average hunan style chinese
Brookville Inn: gourmet dining can hit at times and miss also
Olney Ale House: burgers, wings, ribs, beef stew, homemade bread, large beer selection on tap
Sole de Azteca: pretty high quality tex/mex/salvadoran, try the seafood soup and chile relenos
El Andriega(Ashton) : also high quality tex/mex/salvadoran, mariachi band on weekends
Olney Grill: good stir fries, salads, burgers, ribs, pub style cooking, The best white crab bisc in the world, decent crab cake, Blue Moon, Guiness on tap, good to watch people
Pana Thai (Derwood): very high quality Thai food in a non descrpt strip center
El Azucar: (Layhill): outstanding Salvadoran/tex/mex...The best garlic infused whole crisp fired red snapper I have had anywhere including mexico.....all you will leave is the bones, very large and good ceviche
re: dining with doc
dining with doc pretty much covered it. Le Manenequin Pis is hands down the best choice if you can get a reservation. If they have the mussel safron soup, you must get it.
Right next to it is a decent sushi place, Wasabi Zen.
Olney Grill is OK, but nothing special. Great crab bisque however.
BJ Pumpernickles is quick, friendly, and has very much the NY style diner. Steer away from the 5-layer cakes however, they tend to be dry. Good whitefish salad, and very good sandwiches.
Love Azucar, but the service can be hit or miss.
However, I'll add a few.
El Napolito in Plaza del Mercado is good, but go for the non-Mexican foods, especially the seafood and the lamb chops. They also have a great chile releno. Most of their typical Mexican fare is just that typical, but their seafood is outstanding. Ask for grilled vegs. as your side or you will get black beans and rice, even with the non-Mexican entrees.
If you want gyros, House of Gyro at the corner of Norbeck (Rt. 28) and Georgia Ave has pretty good ones, but the place is very minimalist. In the same small shopping center is a Jamacian place that is pretty good, a Korean restaurant that has a name that is in Korean only so I can't tell you what it is called, and a decent, but not great Thai restaurant (Thai Tavern)
Olney is not a food mecca, but my preferences, in approximate order:
Mannequin Pis is priciest and maybe not as good as it once was but still has very good for mussels and Belgian beer
Sol de Azteca is underrated: Tex-Mex and some good Latin dishes
Riccuiti has best wood-oven pizza and some other Italian
Olney Ale House rustic atmosphere, OK comfort food, good beer and right across street from theater
Blue Moon and Olney Grill decent middle-of-road American fare
Pumpernickel's mediocre deli but with huge menu to suit any taste
Hunan Delight the best Chinese food in Olney (FWIW)
Inn at Brookeville Farms: A puzzle - great atmosphere, sometimes very good food and sometimes bad, the cheap pre-theater menu is usually a good deal, not sure if still offered
I'd definitely skip all the others in Olney.