I thought I might give a quick first impression review:
I have changed from a 2 year old HTC Desire HD to this I9505 16GB S4
The change has been a smaller jump than from my previous Nokia N85 which was a non-android and non-touchscreen smartphone.
Really the Desire HD could have served my needs OK for a couple more years.
So why change, was it really worth it?
Well, the S4 does have a bunch of extra features and higher performance.
The quad core 1.9GHz processor does enable it to do things quicker and easier.
The camera is better and my old Desire HD did not have a front facing camera.
The S4 has a noticeably better speaker than my old HTC had, something I had noticed with one friend's S2 and another friends S3 - better sound than my HTC.
The screen - just wow!
The battery with the higher capacity is much better too - I'll charge every night and most likely never have an issue with it.
So yes, both are touch screen pocket computers running Android and my new phone is being used for mostly the same apps that I ran on my old phone. Sure, changing phones isn't strictly necessary and if I didn't have the money I would have been OK on the old phone.
But I am happy with my new phone with better sound, better camera, better screen and more powerful processor - it is a nicer experience using the S4.
I also plan on using the NFC for paying for stuff once it is available on my phone in this country.
Overall I'd say that if you can afford it you wont regret updating the phone to the S4.