Round Corner reminds me of a mullet that's a party in the front, business in the back. The front half is purely a bar--there's three or four small tables that serve as drink stands, the music and conversations are loud and it's dim (almost dark). But in the back there are tables and chairs, a quieter atmosphere and they actually serve up some decent tex-mex dishes.
When I'm there for food I always go for the pozole and steak tacos; happy hour tacos are half off (sha-wing!). The Tijuana Street Dog, a bacon wrapped hot dog slathered in all sorts of wonderment deserves a national holiday, but I save that for special occasions because I try to be nice to my arteries (sometimes).
When I'm there for drinks I get a mojito or margarita. Margaritas lean towards the salty side but are also tangy and refreshing; great combo with Mexican food and served in boho-chic jars. Their tequila selection is so-so, I mean, I really expect more options if you're going to devote a fourth of your drink menu to a particular liquor.
Make sure to bring out your best manners when ordering up at the bar, the bartenders can be a little rough around the edges at times. And it's in Lawrenceville so you can expect a pretty hip crowd, especially weekend nights.