Quark's is set amid the Star Trek Experience at the Las Vegas Hilton. It caters mainly to science fiction fans eager to live out their dream of having dinner and drinks on Deep Space Nine (where the 'original' Quark's Bar was located). As would be expected, the food and drinks are all Star Trek themed. The Warp Core Breach, for example, is one of the more popular drinks and comes in a massive fishbowl with steaming dry ice. The servers wear Star Trek costumes and you'll be sure to enjoy roaming Klingons, Vulcans, Ferrenghi, and other races. Quark's sits adjacant to the Star Trek gift shop, so you'll be convienently able to browse while waiting for your food to arrive. Their official website can be found here.
With the emphasis on theme, you might be surprised to learn that the drinks and food have gained a good reputation. The menu is limited, but has a variety of salads, sandwiches, pasta dishes, and hamburgers. They serve large portions of entrees that match the huge drinks. The atmosphere is more suited to groups and parties than a quiet dinner. With the unusual number of roaming staff and gawkers, it can get quite noisy. Quark's is definitely not the place to bring your loved one for a romantic date, unless they happen to be a die-hard Trekkie!
There is an actual bar at Quark's as well, so those hoping to just have a drink and soak in the scenery can be accommodated. Given the rather high prices (even for Vegas), I would advise those doing Vegas on a budget to avail themselves of the bar and split one of the over-sized drinks.