We ate lunch there on our last two trips. We split our stays between the Poly and the BWV, and during the first part of our trip we would visit the MK and then hop on the Poly and have lunch at the Concourse Steakhouse.
While I wouldn't rave about it, we did enjoy ourselves both times we went. There is nothing overly special about the restaurant, but it's nice to be sitting inside of the Contemporary and watching the monorail coming through.
The service was good, and the food was very good. It's just basic lunch fare, although there are different options available. My wife had a burger and I think I had a cheesesteak. DD had a grilled cheese and DS's had chicken wings. The shakes were really good.
Overall it's a good place to have lunch. It's not expensive, and it's nicer then just grabbing a burger in a fast food type place. The convenience of being on the monorail is a plus also.