The end result is a mixed bag. Some of the stuff is legitimately innovative and valuable, like the phone's Multi Window mode -- as seen in Samsung's Galaxy Note II and other existing devices -- which lets you view two apps side-by-side on your screen at the same time. It works only with a limited number of apps, but those apps include programs like Chrome, Gmail, Google Maps, Google Talk, YouTube, Facebook and the system Messaging app, so it has a pretty wide range of potential.
Also noteworthy is the GS4's Smart Scroll mode. When enabled, it allows you to scroll through a Web page just by tilting your head gently up or down. Cool factor aside, it's easy to imagine scenarios in which it'd be handy to keep one hand free and make on-screen text scroll with a simple tilt of your chin.
The caveat, like with many of the Galaxy S4 features, is that Smart Scroll is very limited in where it can be used: The feature works only in a Samsung-customized version of the old Browser app (not the superior and actively developed Chrome for Android application) and in a Samsung-customized version of the Email app (not the more feature-rich Gmail application). It also doesn't work well in dimly lit environments, since it needs to see your eyes in order to function.
The Galaxy S4 also includes S Health, a program that takes advantage of a built-in pedometer as well as temperature and humidity sensors in order to offer a suite of health-related services. These could certainly appeal to the FitBit-using crowd, though their accuracy was inconsistent in my experience: The S Health Walking Mate function frequently forgot how many steps I'd taken in a day and reset itself back to zero. The pedometer function also doesn't work too well if you carry the phone around in a bag or purse instead of your pocket; in those scenarios, it tends to dramatically underestimate the number of steps you take.
The GS4 can also be used as a universal remote to control your TV and various entertainment center components. The setup process is simple and the function works well.
And the phone features a new Easy Mode that allows you to trade the typical home screen environment for one with fewer options, larger icons and an overall less daunting layout. It's certainly not something an experienced user would want, but it could be valuable if you were configuring a device for a less tech-savvy smartphone newcomer (like a parent or grandparent).
Beyond those items, most of the Galaxy S4's software elements err on the side of gimmicky, with fleeting novelty but little lasting real-world value. Some examples:
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