It seems somewhat perverse to buy an expensive, slim, beautifully, elegantly designed object then sheath it in a cheap and relatively ugly, bulky plastic case. However, in the interests of protecting the expensive beautifully designed object, that's what many of us choose to do.
This one is pretty good. Although no thing of beauty, it is a good fit and is robust - I dropped mine down a flight of metal-edged stairs and the case took a couple of dents but no damage whatsoever to the phone.
It's thoughtfully designed with the apertures for the camera, dock and buttons all sensibly sized and in the right place, and it's relatively compact so doesn't add too much bulk when it's in your pocket. The two parts fit together well and the build quality is good. So all in all, fit for purpose, it does a good job and I'd recommend it.