I recently bought a very nice Case sheath knife that also happened to come with a very nice Case sheath. I paid quite a bit for both, but I wouldn't have sprung for either if they hadn't come as a nice and appropriate package. All good sheaths should have some common features, IMHO. Assuming decent quality finished leather, first on my list is that the sheath part covers most of the knife, including a large portion of the grip, that it have a secure flap cover that keeps the knife from falling out accidentally, that it have a sturdy belt loop, and that it have some kind of liner in the sheath. As long as it has those characteristics, I'm pretty happy.