Hi Sam - Big Run is mostly known for the quality of the stumps it has in the woods along the north-side of the stream. It's not really one you want to fish, unless you are willing to enjoy modest fishing and
great views of stumps.
Since I'm not a stump enthusiast, I consider Big Run to be fairly unimpressive compared to literally every other stream in the entire park, ever. Well, NF Thornton was kind of obnoxious in figuring out how to legally park, so I guess it beats that one even though there's an ice cream shop there.