I lived in Chambersburg for 6 years. The whole dining scene is a pit of mediocrity aimed at fleecing clueless yuppies from Mill Hill and Princeton in search of some kind of Ethnic flavor.
Having said all that, your best bet is Amici Milano. For Pizza try Delorenzo's pizza (there's also a Delorenzo's steakhouse which is excellent..aged steaks) or Joe's Tomato Pie.
Stay away from Diamonds. It obscenely over priced and the food is so-so. It might be worth it to go down there for drinks and check out the low rent "Sopranos" wannabes at the vinyl clad bar.
In Chambersburg PA, Bruno's on Orchard Drive is our favorite. Lots of different delicious soups, buffalo chili, good sandwiches at lunch. Busy at lunch, closes around 1:30. Open for dinner only Fri and Sat (maybe Thursday too) when the chef gets more creative with the specials. They do takeout, but the place is so nice, small, and usually quiet that it's always a pleasure to eat there. When we're there for dinner we have soup or an appetizer, main course, dessert and coffee for apx $40. They sell their frozen soups for $5-6 a quart and we always stock up. I am a good cook, but I can't make soup like this! This place is atypical of central PA restaurants--the folks at Bruno's know how to cook.
Also on Fri & Sat Jim's Farmer's Market has Amish food stands selling ham sandwiches, fried oyster sandwiches, London broil sandwiches, fresh soft pretzels, lemonade, baked goods, candy, fresh vegetables, meats and cheeses. Kind of fun.
We haven't been to Oki International for a while. Indonesian food in a small family-style place a block or so south of the square.
For a splurge, try the Mercersburg Inn in nearby Mercersburg.