Good restaurants:
Delicious
Yummy
Excellent
Expensive (usually :P)
OK restaurants
Satisfactory - meets standards
Meh (colloquial for "nothing special")
Bad restaurants
Unappetizing
Distasteful
Other
Unique - when restaurant offers something out of the ordinary
Homely - usually for family-run restaurants, a very comfortable atmosphere
Romantic - restaurants people go to on dates, dim lighting, usually shared dishes
Exquisite - tends to be reserved for higher class restaurants
Lovely - replacement that is a bit better than "great" if you've been using great too much