The old part of the city has a good selection of restaurants. There are also touristy types of streets: full of cheap, reasonable-to-poor quality restaurants (very similar to those streets in the Latin Quarter in Paris). If you wander around to the quieter streets, you may find better French places.
Dress Code: Shorts and t-shirt were what I wore. In the more exclusive places, you may need to dress up.
Lyon is renown for having more restaurants per square metre than any other European City. Its gastronomic specialities can be found clustered in the Part-Dieu quarter while in Vieux Lyon, traditional bistros are more the order of the day.
Aux Trois Maries... One of my friends was named Maria, and after drinking there for a while, we felt like the 3 Marias. :-)