Shiny = bad. That is the collection of excess oils that are on the surface.
Leather, when it is new and fresh, is matte, and is soft and supple. If you have a sedan with leather seats and don't know what the new leather feels like, the fold down rear armrest should provide you with unused leather that you can feel. Clean and well hydrated leather should look and feel just like that. You'll notice that it is nice and matte.