This is here to give you all a quick read about the differences between the GS3 and GS4. I will state this before anything else, I do not own a Galaxy S4, I have owned a Galaxy S3 as well as a Note 2 so I am very familiar with the software on the GS3. Without spoiling too much, not much has changed but there are some differences in the hardware and software. I will be looking at the basic differences, the ones that you will experience and see on a daily basis.
The Build and Display
As you can see from the picture above, their are differences. While these differences may appear to be slight, they do make the phone very different. The S4 is packing a 5" 1080p display while the S3 has a 4.8" 720p display. The best part about the S4's display is that it is bigger than the S3 but doesn't sacrifice the overall size of the device. It feels the same in the hand because there is less bezel space around the screen as you can see above. Also, you can see slight changes to the design of the plastic and shape of the home button. Aside from that, everything is in the display. Since I don't have an S4, I can't tell you about the differences in colors, clarity and brightness of the screen but if it is anything like other 1080p displays on the market, it will be leaps and bounds better than the S3.
The biggest change here is going to be the addition of the Snapdragon quad core CPU clocked at 1.9ghz, or and Exynos octocore CPU which is basically two quad cores linked together. This is the major difference that you would see on a daily basis. Other than that you have the same 2gb of RAM and same storage options. The battery has been upgraded too so that it can power the 1080p display and the quad core CPU. The Camera has also been beefed up. The S4 now has a 13MP shooter while the S3 has an 8MP. Based on what I have seen, the new camera is vastly superior and snapping pics based on camera performance alone, not playing around with features.
TouchWiz hasn't changed that much, the differences that you will see are actually based on the newest revision of Android, 4.2.2. The S4 is running the most up to date version of Android (kudos for learning Samsung) and the S3 is running 4.1.2. That means you will get a drop down will all your toggles that you can customize such as WiFi, Bluetooth, GPS and volume among everything else that can toggled basically.
Different toggle setup than what you are use to on the S3, but if you have used Android 4.2.2 then you are familiar with this set up for the most part. The next biggest change is the settings. You will now see your settings being grouped by tabs as opposed to the traditional way of having everything in one big list that is broken up by headings. You will now be able to pick the area of the settings you want to go to without having to navigate through other areas.
Personally I like this idea and I wish that more phones would implement this. While others may dislike it and want to stick with traditional Android settings I do like the separation here and it may be easier to follow, especially if you are a new Android user.
The next thing that most people will find different are the new camera features. You have a plethora of features to play around with and I will not do them justice until I can play around with them myself. While the S3 had features to its camera, this is the area that Samsung packed the most amount of features and ensure that it had its best foot forward when it comes to the camera war.
You also get the ability to wave you hand to interact with the phone, have you eyes control the screen and control you TV. All new features to the S4 and probably stand outs when showing your friends, family or coworkers but in my opinion more for showing off than actual function (with exception of controlling the TV).
While there is a ton more features than what I mentioned here, I find these to be the ones that common users will use on a daily basis. I also have not had the opportunity to play with the S4 yet so I can't comment on other features that I might be missing. In the end, I find the majority of the features to be gimmicks like the air wave feature and the smart scroll but that's just me.
Word of advice... Play with your phone, its the only way you will learn all these features. Yes its a lot and you could be overwhelmed but take a day or two to play with everything and find what you like.
Updated by creccaj, May 14 '13 @ 12:13 PM.