Big River Grille is okay, IMO. We had a late lunch there in Oct because DH was told on the golf course that their beer was good. We walked right in without a problem at 2pm or so and it was mostly empty. It was a tad warm so we ate inside and the smell at first is very strong - it's the beer fermenting smell. I will say that after about 10 minutes you get used to the smell. They also have some outdoor tables.
The food was decent. Nothing special, but okay. I had a pulled pork sandwich and it was good - the chips are kettle chips which I like. DH had a burger, it was good, and my mom had a salad.
Service was good, and prices were fair. It was nothing big, we likely won't return unless we just need an easy place to step into for a quick meal as there are so many cool unique places to dine at WDW but it was good.
The atmosphere is looking at big beer things (you can see where they make the beer).
I think a large group would be fine there =)