Best mixed drinks and a classier, intimate lounge near the Capitol. The bartenders understand what they are doing and are always helpful and friendly. At some point during the night, I usually end up ordering a Martini Flight, which is a great way to sample Opus' signature martinis. They only have a few beers on tap but they're always interesting choices -- Lindeman's Framboise comes to mind. They also serve decent food with a definite Japanese influence (edamame, grilled eel rolls).
I do wish their seating were more comfortable. The little seats around the low tables are extremely light and prone to tipping over. Sure makes it harder to relax and partake in martinis.