Terrible. Nothing unique or interesting about it. This place might have been impressive 50 years ago when there was nothing else to eat in Pittsburgh, but nowadays it's just boring, overpriced, and well past its expiration date. But if you like the taste of grease and canned cheese sauce, you'll love it.
On any given Saturday night, you'll often see greasy brown half-full bags of fries littered around Forbes Ave. These are the leftovers of drunk kids who got scammed into buying a laughably excessive order of fries when all they wanted was a handful to go with their hot dog. "Quantity over quality" and "waste for the sake of waste" seem to be time-honored traditions among Baby-Boomers around these parts, but anyone born after 1980 will likely be more disgusted than impressed.
The visible contempt they have for their customers is not at all charming like it is at a place like The Wiener's Circle in Chicago or other old-school dives wit genuine character; it's just alienating and sad. The O belongs to a class of old-guard Pittsburgh eateries that should have folded years ago, but is kept on life-support by a handful of deluded old yinzers who refuse to change with the times. Skip it.