This is just my opinion.
To me, the big river at the boardwalk isn't as good as some of the other big river locations. I think that because it is in such a touristy area they are more conservative with the beer they brew - it is mostly lagers and easily accessible beer. I sort of like the stout they have at some of the other locations, but I've never seen it at the boardwalk big river location. That sort of makes sense when you realize how touristy wdw is - a lot of people probably don't even realize that it is a microbrew, they probably come in thinking of it mostly as a restaurant. Which it probably is. They have a pretty decent wheat beer in the spring/summer, but it isn't my favorite wheat by a long shot, but it is pretty drinkable. Also, the rocket red is pretty good, it is a little hoppy and I would be happy to drink it most any time. I'd be happy to sit outside and have a beer or two and a burger most anytime, but the beer isn't really *great* but it is OK. It is nice enough most days to just enjoy the location. If I was really looking for food on the boardwalk I'd go to flying fish or maybe even spoodles, but for a burger and beer big river is OK. I kind of think of it this way. Big River isn't a microbrew so much as a disney mid-range restaurant themed as a microbrew. Similarly, ESPN club isn't really a sports bar so much as a Disney mid-range restaurant themed as a sports bar.
Edited to add- I do think that the quality of the beer at big river has gotten better over the last few years with time