I like Mossy Creek. And, yes, it is a challenging stretch of water. Mostly because of the pressure the fish get.......they've seen most anything you'll throw at least once. But tough streams help you become a better caster and a better fisherman. If you can figure out what is best to throw, then present it in a way that gets the fish to take, all on a tough stream, it makes you a better fisherman. Mossy is definitely worth a trip.
You may also consider travelling a little farther to Buffalo Creek. It, like Mossy, requires the same kind of landowner permission that Mossy does, which you can now get online (https://www3.dgif.virginia.gov/troutpermits/). It's a little different than Mossy in that a good section of it flows through what you would consider "mountain stream" conditions. Last time I went there I caught 20 fish, mostly rainbows, on pheasant tail, caddis, and copper johns.Both streams are fun.