I've been several times. It is a typical New York Street Festival completed with underwear and used blue jean vendors.
While there are some unique food vendors at this particular festival, for the most part the festival now contains the type of food that one finds at any number of Manhattan Street fairs: Italian sausage vendors, middle of the road Ameri-Thai, elephant ears and such. There will be some of the restaurants along Ninth Avenue participating. Of note will be a couple of gaucho style steak sandwich vendors in the 40s, and some pretty good Greek bakeries in the 50s. The festival is not nearly as unique as it once was in terms of serving as a good barometer of what a great ethnic restaurant neighborhood Hell's Kitchen is. Don't hesitate to explore the restaurants lining the streets behind the festival vendors. There are some great places in that stretch including Peruvian, good by NY standards Thai, the only burger place I would recommend in NY (Island Burgers and Shakes) and Cajun. I've been gone for six years, so there is definitely more than I could ever recommend there now.
My one piece of advice would be to get there early as the whole fair just gets jammed with people as the day goes on.
New York is always fun and the festival has no entry fee. You simply pay for what you eat. You can really see the entire festival in a half day if you get there early. So make some other plans to do other things for the rest of the weekend.