We tried several of the Tacos at R&R; they were good, and possibly some of the best in the DC area that we have tried. Nowhere near the best (I'm on the west coast a lot), but definitely very tasty. We heard the lamb tacos were very good, but we a little disappointed by that one. The chorizo was good, but the carnitas were even better, although a little too greasy/fatty. The location is small with little seating on small counters, but the whole "hole in the wall in a gas station" is unique.
My issues were with the service; the girl who took our order we couldn't understand well and it seemed like she didn't want to even be there. We waited a long time for our tacos, and after we ate them, we wanted to try a few more. On the second order, we waited about 20 minutes and then had to go to them to remind them about the order. When I was explained it to the girl, she started getting mad at me and actually blamed it on us for not getting the order in. She couldn't speak English well, which made it more frustrating for us.
So my advice is: If you're in the area, grab some tacos, but take them to go. They are good, so you should definitely try them out. But have some time on your hands for the wait.
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