[Galaxy S 5 Q&A, Help & Troubleshooting] Master Ramy:
Lets not forget, Samsung only focused on 5 main parts, the rest will only be shown through later Hands-On tours and trying out the phone for a while. most software wasn't even discussed, there's still much more features and Samsung stuff that we haven't heard about yet.

Nonetheless, here's a brief comparison of the devices, off the top of my head, as of what we know right now.

Screen Res: S3:720p ----> S4:1080p--->S5:1080p (No change)

On the above note; PPI is not MUCH less, its only a difference of .1-.2 inches in the screen, so no, not a major PPI difference. I doubt we will have any ability to see pixels with naked eye.

Processor: S3: 1.4Ghz ----> S4: 1.9Ghz ----> S5: 2.5Ghz (Roughly equal improvement, makes sense)

Camera: S3: 8mp ----> S4: 13mp ----> S5: 16mp + new flash tech and possible ISOCell incorporation, professional DSLR chip usage, selective focus. (Major improvement)

Screen Size: S3: 4.8 ----> S4: 5.0 ----> S5: 5.2 (Natural improvement)

Video Recording: S3: 1080p HD video ----> S4: 1080p HD video ----> S5: 4k Video. (Excellent improvement)

Build Quality: S3: Plastic build with flimsy back, rounded. ----> S4: Plastic build with flimsy back, metal lining around edge, not as rounded ----> S5: Plastic build but soft touch back and waterproofed IP67, about as rounded as S4(unsure on that last bit, will reserve judgement till I see it.)

Battery Life: S3: 2100 MAH ----> S4: 2600MAH ----> S5: 2600 MAH (Ultra power saving mode, black and white screen, further dimming, much better overall battery management) (Major improvement in a very important category.)

TouchWiz UI: S3: Nature UX, somewhat cleaner than previous versions ----> S4: Improving the UX, a bit cleaner but not much difference outside of more samsung features thrown in and more clutter and tabs on settings apk (which most hated) ----> S5: Much cleaner and toned back look, but no word on any MISSING features, just that they are not as haphazard and thrown in everywhere in the device; everything is still there, just much smoother and faster and better on the eyes, making us actually possibly LIKE touchwiz.

Connectivity: S3: Newest tech of the time ----> S4: newest tech of the time (next Gen) ----> S5: newest tech of the time (3rd gen from S3 + Download booster to combine LTE and Wifi for much better combined speed.

SD Card Slot capacity: S3: Up to 32GB ----> S4: Up to 64GB ----> S5: Up to 128 GB

Android Version: S3: Android 4.1 Jellybean ----> S4: Android 4.2 Jellybean ----> S5: Android 4.4.2 Kitkat.

Hardware extras: S3: Nothing comes to mind ----> S4: IR Blaster ----> S5: IR Blaster, Fingerprint Sensor, Heartrate Monitor.

This is all that I can think of off the top of my head. I'm sure more will come to me and I will try to update this post, but this shows that its actually a Bigger improvement than we think at first.

All this is to say, the usual incremental upgrades are there, plus cleaning up design, making touchwiz likable, water proof, adding finger print sensor, MUCH nicer Camera, Nicer processor, many fancy additions in the sensors for the camera, heart rate sensor, newest version of android, and no doubt a TON of software things that we still have no clue about and that we will discover as the devices begin getting in more hands.

Hope this clarifies my point.

~ Master Ramy