Rat's is indeed great, and check out Kafe Kabul there. Great place that is very romantic on a winter night when they have the fire place burning. In the summer time, we like to sit outside behind Kafe Kabul near the pond and enjoy the sites. Great place!
The Ferry House in Princeton is also nice, although I don't know if I would consider it romantic. Witherspoon Grill is nice for outside dining, but again, not sure if I would go so far to call it romantic. It is a great place to people watch though, along with Blue Point Grill. We also like outside dining at Tre Piani in Forrestal Village, but there is nothing romantic about the inside. -mJ
Princeton restaurants are not what one would call romantic.
I imagine you are looking for a quieter place, good ambiance, secluded seating or less crowded tables, maybe with a view, etc. If that's the case, some considerations in the Princeton area (in order of distance from the center of Princeton) would be:
-- Acacia, Lawrenceville, NJ
note it's BYOB.
-- Rat's, Hamilton, NJ
-- The Inn at Phillip's Mill, New Hope, PA
-- Pluckemin Inn, Bedminster, NJ
Rat's is definitely romantic. I like the food, although I think some of the more dedicated foodies might quibble. However, if you go on a nice night and you make sure to tour the lovely sculpture park before or after dinner, it's wonderful. The service is great, the atmosphere and decore is lovely, the food is tasty. However, that said, check out their menu beforehand. I am not a seafood fan either, and their were a few seafood dishes on the summer menu. When I went recently, though, I had an absolutely spectacular venison entree, which was one of their specials. It was a venison tenderloin (?) with a molasses chili sauce. Tender, smoky and just a hint of sweetness. Honestly, I can't think of a more romantic place - unfortunately, I was there with my father on this last visit!
Looks like Rat's is not offering their dinner menu on Sunday evenings?!
Website says "The fine dining menu is not available on Tuesdays & Sundays during dinner hours. Only the Kafe menu will be offered." OP may want to call Rat's to confirm. If that's the case, may want to consider Sunday brunch here instead.