To me the definition of beauty in a rifle or shotgun is its lines. Hard to describe, but the lines must "flow" and seem organic somehow. The best also have well figured wood that was chosen to enhance the flow of the design, especially through the wrist area of the stock. I like engraving, if it enhances the over all design and does not simply call attention to itself.
I can appreciate function only, and have a couple of rifles and a shotgun that are just tools. They are made of the most durable materials and work well under extreme circumstances when proper care is not an option.
But hunting is too important to me, and life's too short to hunt with an ugly firearm. Favourites of mine that have beautiful lines are my Krieghoff Hubertus single shot (Kipplauf ) rifle, an AYA model 53 sidelock side x side shotgun, a Brno 22F full stock carbine, and a custom Brno ZKK 600 30-06 that was restocked in the style of a British stalking rifle my a master Canadian gunsmith. And a Thompson-Center Muzzle loading rifle in the Hawken style.
So the style of my guns are German, Spanish, Czech, British, and American. I don't think any culture has a monopoly on beauty.