Tasty and refreshing, like you want from a ginger beer highball. Ginger flavor rules here - I also pick up a hint of the minty flavor from the Nardini (complementing the ginger). I used Bonal (no Bryyh on hand) - it gave a small bitterness in the during the finish, did not linger. I couldn't pick out the spicy notes of the rye with the ginger and Nardini, but the high proof kept the cocktail interesting without seeming boozy.
I'd been looking for a good use for this bottle of Byrrh I picked up recently, and I think this is it. No Nardini Amaro but Averna is similar to the description Simon gives for Nardini. No Thomas Henry so used Fever-tree ginger beer. The liquorice, caramel and cola flavors from the Amaro blend splendidly with the spices from the rye and the ginger beer. And it looks just right for World Goth Day. B.t.w., WHERE (at which bar) in Denver did this originate? Any clues? It's a big city....