I hope nobody will be offended when I express my opinion that they all look awful. The watch was the last thing that needed a case, not on your wrist like that, any additional material is too much.
I feel quite the opposite.
I am a bit of a watch fanatic and have many, from fine dress watches to rugged sports watches to a couple of "smart" watches.
I personally like the rugged cases (the Spigen ones) on the Apple Watch. Makes it look vaguely G-Shock-esque.
I like that you can wear it how you want to - make it look like a rugged sport watch or a dressy chronograph or a tricked out smart watch, depending on your mood.
On a more practical note - I have small scratches and digs on most of my watches.
For a smart watch, that isn't going to change - a case makes perfect sense.
Slight scrapes and bumps into walls, desks, etc are part of life - why ruin a perfectly good piece of tech if there's a way to stop it?
In saying that, I know a lot of people that think my G-Shock watch is a monstrous and tacky piece of tack that shouldn;t see the light of day, so everyone has an opinion on everything...