MAK,
Just a small correction to what FF has posted. Dahlemer Binz used to be a great favourite of mine. Just a 30 min hop over great scenery to a great location and a cosy spot for lunch. Still has the great scenery but unfortunately the restaurant is closed for the moment. (New owners haven't figured out what exactly they're doing yet.)
Koblenz certainly rates highly .. especially if you like Greek food.