I've been to Quark's twice, most recently taking some friends who had never been and were up for something different. If you are (like me) a Trek fan, or just (like my friends) up for something different, this is a nice place to have a meal.
The decor and theme are unique, and the Star Trek references in the menu are cute. The food is good, relatively inexpensive, and many have a twist that makes them a bit different from the average menu. I enjoy the Flaming (literally!) Ribs of Targ and the blue Romulan Ale. Service is good (but not exceptional).
The only real downside I've experienced is that I find the mingling Trek characters a bit embarassing and annoying. But that's a minor complaint. As someone else said, this isn't a "must go" place, but it is a bit of fun once in a while.