I also say apple may be boring to some, cannot customize it, etc. however I say it works.
First the good about s4, the screen is nice, big and looks great.
I tried out an S4 Active, coming from a 4S. Partly just to try it out, but I was looking for more screen real estate as well as hoping to try out wireless charging.
I chose the Active over the S4 for the screen; S4 screens were too dim and too "warm" (biased toward yellows/reds); the Active's display was more color neutral.
Bloatware. Holy frack I'd forgotten how bad carriers were with loading a bunch of cr@p on their phones.
Larger display was nice, yet disappointing. Video was nicer on the larger display, and the Kindle app made good use of the size too. Most everything else simply presented the same amount of content as my 4S, just using bigger fonts/icons/spacing.
I could get over various ecosystem related limitations (no iMessage, no Airplay, poor Reminders implementation even with 3rd party iCloud sync, etc.), I could tolerate the overly sensitive touchscreen edges (even with the extra sensitivity turned off), I could get over the complete absence of an Amazon Prime Instant Video app, but three key issues drove me to return the device:
- Wifi dropouts at work - wifi worked fine at home, but at work any apps seeking network access after a device wake-up would freeze until I toggled wifi off/on. iPhone 4S 100% solid with no issues. Having to screw with wifi is unacceptable, I should be able to just leave it on.
- Couldn't dial-by-voice via bluetooth without touching the phone; voice command of "dial 834-321-1234" resulted in a screen pop-up seeking confirmation. I shouldn't have to fish the phone out of my pocket, unlock the display, punch in my PIN, then confirm the command. Maybe that was configurable somewhere but I was just about ready to return the device due to:
- No lock screen notifications when using PIN device lock (work Activesync policy). Seems to be a Samsung thing; any changes to lock screen widgets were disallowed if PIN lock was active. If I deleted my work Exchange account, turned off PIN lock, and set up an alternate lock screen widget (tried a couple different ones) it was great until I added my Exchange account back, it forced PIN lock, and Samsung switched things back to the basic clock lock screen.

I bet these could have been solved with different ROMs, hacked applications, rooting the device, etc. Trouble is I have other things I'd rather spend my free time doing and there were no killer features or killer apps making me want the device badly enough to invest that time to make it conform to my usage requirements.