Temecula can be a bit tricky. I'd say most of the restaurants will be a disappointment, especially if you are from a large metro area (i.e. LA, SD, NY, SF). However, there are some good places:
Wineries in order of preference(for food) - Wilson Creek, Pointe, South Coast
Pizza - Bella's in Murietta (I recommend ONLY the NY style Pizza, if you order anything else, you are on your own), the crust is fantastic! When we go, we order pizza and drinks.
Hanna Sushi on Hwy 79
Chinese?...uh, not so much