The body is still dominated by softly molded plastic, and the S 4 doesn't really advance the aesthetics of its predecessor the way competitors Apple, Sony and HTC have done with their latest phones. Apple and HTC, in particular, have put a lot of sweat into machining metal into jewel-like enclosures; Samsung doesn't seem to care all that much about looks.
Samsung does care about trying to push the envelope on what the phone does, but it may have poked through the envelope, tearing a hole or two in it. It's probably not a disaster, because most of its features can be turned off, but first-time users could be confused.
For one thing, Samsung is taking the whole "touch screen" thing further by now sensing when the user's finger is hovering over the screen. In other words, you don't even need to touch the phone to make it react. Hovering over a thumbnail of a picture in the Gallery will reveal a bigger thumbnail, and hovering over one email in a list will show a preview of its first lines.
The idea is similar to the "mouse hover" feature on a PC, which sometimes reveals things before the mouse is clicked. Implementing it on a smartphone is trickier, though. On the PC, you have to use the mouse, so you'll discover the hover functions in the normal course of use. But since the feature is new in a smartphone and there's normally no reason to have your finger hovering over the screen, users are likely to discover this feature by chance. That wouldn't be so bad if all applications responded to hovering in a consistent manner, but very few applications react to it all. On the S 4, the "Email" app will show previews, but the "Gmail" app won't. The built-in "Gallery" app will show picture previews, but other photo apps won't. I suspect users will get tired of trying to hover with their fingers and give up on the whole thing.