In planning our trip to Oshkosh we didn't find much in terms of helpful restaurant reviews. Most of the local press covers the chains, but I don't look for an Applebee's or Pizza Hut when I'm travelling.
I'd be willing to recommend two places that we tried.
The first is The Vintage, located in the Hawthorn Suites hotel. The room was surprisingly nice for sitting off a hallway in this family hotel, a pool full of kids two doors down. Our expectations were low given the setting, but the food was decent. California/Mediterranean style food with a few high points (a wild mushroom ravioli that was nicely done), and very reasonable bar and wine list. Two courses and a drink came in under $30 a head. If I was looking for a quiet meal I'd consider going back.
The second is Fratello's, a restaurant affiliated with the Fox River Brewing Company, on the river. The dining room wasn't too noisy even on a Saturday evening. On a long summer evening I'd probably want to
sit outside. Well prepared, creative food served in big portions, accompanied by some pretty good house-brewed beers (in Wisconsin I found that the German style beers seem to be best). The cashew-crusted walleye was quite tasty. I would definitely go back to Fratello's on a future visit to Oshkosh.