I grew up watching Lidia's TV show as a kid. So of course when I found out she had a restaurant in Pittsburgh I just HAD to try it out.
The biggest selling point of Lidia's is probably their service. People say ti's a good "date spot" mainly b/c of the atmosphere and service. Their wait staff definitely has been trained to the attentive, but at times it can be overly done and I feel like I'm a part of a weeknight sitcom.
For appetizers, get their grilled octopus. I've heard good things about their chicken livers, but I've never tried it myself. Their fritto misto is prepared well, but not excessively special.
Their pasta tasting trio is always a great way if it's your first time at Lidia's; they always have two house-made pastas and one imported from Italy. From my experience, I've always enjoyed their housemade varieties, especially their pappardelle and gnocci (when available). Their ravioli's are typically pretty good too. The imported pastas just don't seem to reach that perfect al dente "bite" fresh pastas can achieve.
Their ossobuco is a giant braised lamb shank that is fork tender and flavorful in a dark rich sauce. It seems to be a popular dish, as the last time I was at Lidia's they were out of it.
On an ending note: Lidia's does take reservations (just visit their website or hop onto Opentable and rack up those dining points), but I've never had an issue getting a seat without reservations.