The outside of the cover has a rubberised feel to it, which gives quite a lot of grip. Generally this is very good as I find the aluminium on the back of the phone quite slippery, but the "stickiness" can be a bit annoying when you're trying to slip the phone (with cover) into a pocket, etc.
The cover has a slight metallic finish, which I wasn't expecting. This suits the premium look of the HTC 10 very well, even enhancing the bevel around the back edge.
If you're after a cover that offers moderate protection while not detracting from the appearance of a beautiful phone, this would be a good choice.