Regarding Big River here's my 2 cents... if you are a craft beer afficionando with a liking for quality craft beers (be it local or bottled) you will be disappointed with Big River. The beers there are pretty standard (read: boring) and meant to be palatable for mainstream beer drinkers. They have a pale ale, an amber ale, a lager, a pilsner, a brown and a wheat. I tried the Pale, the Amber, and the wheat. They were all pretty vanilla without much hop character.
Big River is a franchise that is owned by the same company that owns Rock Bottom Brewery (among other brewpub/restaurants) and I have the same opinion of their beers. As a matter of fact they could potentials be the exact same beer recipes.
For my money I'd rather track down a dogfish head 60 minute IPA, a Le Fin du Monde at the Canada pavilion or even a Widmer Bros. Drifter Ale (it was available at the pool bar of Pop)!
Here's a thread that lists where to find the better beers at the World.