I may be wrong on some details but this is my impression.
Being water resistant is great for me. There have been many times where I do sports that involve water such as kayaking, canyoning, and jumping in to a river off a cliff etc... but never got to take pictures/videos. Heck getting soaked on a bicycle isnt so worrying now. Now I can sort of if I don't jump into it for too long anyway. Being dust proof is also good, sometimes dust can get onto your screen which is annoying.
The screen is using smart technology to be the best for optimum viewing. That's great and since it is already 1080p and had 440 odd PPI, it's going to be even better on a 5.1 Inch screen. People look at it only being 1080P, but if it went 4K, then battery life will go down. More pixels and size means more power consumption. There's a reason why some have stayed small and kept the pixels low, to their detriment of course. 440 PPI is about the best the eye can see below 8 inches from my memory.
Finger print technology isn't great, but even with it's flaws it is better than not having it. The option is there.
2800 Mah battery is nice, I am a fan of larger capacity. Removable battery means you can upgrade to more too.
Autofocus is 0.3 so the World's fastest. This is handy for people who like to take photos quickly.
Some functions such as depth of field mode will allow funky photos as well as the standard of fish eye, filters etc... in built.
4K video recording is cool. One day there will be 4k TV's as standard. The camera is already decent on the S4 with slow mo, and other features.
128 Gig SD card slot means you can have a lot of storage.
New power save mode to turn things black and white, as well as closing unnecessary features.
The phone has better connectivity, so 4G network will be better since it will be more compatible with other networks (If they start to share etc...) Connection to Wifi apparently will be faster too. Download speeds is something they seem to think will see a huge boost.
S Health with heart rate monitor, temp, humidity sensors seems good. People who do sports may enjoy it more.