It's smaller and more attractive than the original Xbox One.
The Xbox One S is a 40% reduction in size over the (admittedly very large) original Xbox One. The console also just looks better than its predecessor.
It's compact. It's got a sweet design with tiny holes covering half of the front face. It's got a sharp black and white color scheme. Aesthetics are all perspective, of course — maybe you prefer the look of the original Xbox One to the Xbox One S. You're wrong, but you're welcome to believe that!
Just look how much better this thing looks:
And yes, it can be stood up vertically as well:
Of note: the vertical stand is "optional" (which means you gotta buy it for $19.99).