Market Street Diner is very mod and cutesy. The food is decent diner fare, but in giant portions. Where the restaurant really shines is in its pies and desserts. I worked here for a summer when I was a teenager and thought the biscuits and sweet potato fries were pretty great.
I would say Market Street is pretty average, as far as diners go. Not the best, not the worst. You probably won't be disappointed, but also not enchanted or addicted and counting down the minutes until your next visit.