Serious flooding in the city has knocked out a few restaurants most notably Cafe Paradiso which is a real pity and maybe your hotel! A friend recommended Les Gourmandises for formal french but i always went to cafe paradiso when visiting - hope it recovers! And i think Augustines closed down recently.
Although you would have to be very selective about where you ate. We spent a week in Kinsale in June 08 and found many of the places disappointing. For seafood, Fishy Fishy gets all the play but our meal there was, to be polite, underwhelming.
I suspect you'll do better in Cork itself but if you do venture to Kinsale, Max's was the stand-out place.
I agree with Harters, Kinsale has a lot of restuarants but very few are up to much-certainly nothing worth the trek from Cork.
For a city, Cork is limited enough aswell when it comes to dining options. It's been a while since I've been there but from memory, those worth a visit are:
Jacobs on The Mall
Cafe Paradiso ( good quality vegetarian)
Details for all can be found on the menupages link posted earlier.