I live on Mt Washington and love going to the Summit for a drink. They have a long list of cocktails that are creative and use good quality ingredients. Some change seasonally and others stay on the menu year round. I think my favorite is the Spicy Paloma (tequila, fresh squeezed grapefruit juice, and jalapeƱo). My husband is a total sucker for the Old Fashioned here. They also have a nice selection of wine.
I think my favorite aspect of this place is the atmosphere. When the weather is nice, they open the windows that surround the space and it's totally open air. They also have a big stack of board games that you can play while you're there if you're so inclined.
IMO, the only downside is the prices. The cocktails and food are expensive, especially compared to other places in Mt Wash. I recommend going during happy hour from 5-7pm on weekdays - the house cocktails are $6 and beer is $1 off.