This is the kind of place where you're served coffee before anything else. Your placemat is your menu, and the temperature control is questionable. But the sausage omelette features meat from schwartz's market. The ham is freshly sliced off the tinfoil-covered-baked-ham behind the counter. You'll watch your breakfast cooked behind the counter, so you don't have to ask the waitress any details, not that she'd tell you anyways.
My favorite part of O'Leary's is the decor. It's a long narrow restaurant and one side wall is completely taken over by street art. You have the requisite South Side tin ceiling, and there's always tunes playing on the mini-boombox.
The only real drawback of O'Leary's is the regulars. They eye you a bit funny when you first walk in the door. They turn out to be pretty harmless though.