while not truly german, if you love beer, what about Brasserie Beck? They tout their Belgian beer list and may also have something German. Or at least you will know you will have good Euro beer. haven't been yet but the folks on here like the food too.
Another option, strictly for brews, would be Brickskeller in Dupont which has something like 800 beers from all over the world. It's kind of a dive but if you like beer that's your place. But i would recommend doing your eating elsewhere in that neighborhood rich with dining choices.
I actually work right near cafe mozart and have had their food at meetings from time to time. It's not bad and the folks running the place are very nice however I'm not sure it's the right place for a group of friends to catch up and linger.
You could try cafe berlin, which is on capitol hill. I used to work in that area by Union Station and went there with coworkers often for good beers after work. If you or one of you friends is feeling really adventerous you could order a boot of beer. It literally comes in a glass boot, in 2 sizes, I think half or whole litre.
It's not a far walk from the Union Station metro, on the red line.
For a REALLY good beer selection head to Saloon on U Street. Only bar snacks and no standing at this bar, but it's the perfect place to enjoy a good beer and catch up with friends.
I've enjoyed coming to Cafe Mozart for some after work beers. They have a pretty decent happy hour and awesome bar snack mix that I could eat for hours. Too bad I can't remember the happy hour prices, but I can recall thinking that I could in fact justify drinking a liter of beer at such a good price. But that was also after a half-liter of some delicious strong German beer. Note that their tap selection is seasonal.