I've never really thought about rating chain restaurants either.

Hmm.
I guess I just go by whether or not I would return to the restaurant. There are certain chains that I do.not.like.at.all. and there are other places that I adore and we eat there often. I go by price, quality, value - as in the amount of food you get for the money, and overall general service.
We do have a few really good local restaurants, but we have hordes of chains. My favorites are: Ruby Tuesday (I simply adore their salad bar. So good and fresh), Carrabbas, Chilis, Olive Garden, Roadhouse Grill, Bahama Breeze, and Kobe Japanese Steakhouse - which is a local chain.
I'm just not sure how to rate them other than to say they are good.

Four stars I guess?