Ok, so I finally got the Note 4. (My provider is AT&T in case anyone is curious)
Some early thoughts:
1)Screen is definitely NOT night and day difference compared to Note 3. Yes, in many, maybe even most situations when it comes to pictures and videos it is "marginally" sharper and more vibrant. But is it "astonishingly" better? Absolutely not. Bunch of BS hype is what this is.
Text and general browsing is pretty much the same in quality. All that talk about how text looks sharper is nonsense! And don't even start with me. I have a very sharp eye for these things. All that talk about the much higher resolution is all marketing hype. If you have any sense or any care for your money, take this into consideration. The screen is not a reason to upgrade.
2)Overall sound, in calls, speaker, etc. Is NOT any better than Note 3. Phone is still too quiet in calls just like it was. They didn't upgrade it AT ALL! Maybe, just maybe it's "a tiny bit" louder when playing music through the speaker and talking through the speaker phone, and also it seems like the other party can hear me better on the other end. On the note 3 people would complain they cant hear me too great through the speakerphone. On the Note 4, I go no complaints so far.
3)On the Note 3 my GPS would not work for shit. Was told many times it's the AT&T problem, not the phone problem. Besides I exchanged two phones, and it still worked like crap. Wouldn't get my location, sometimes would take 20 min or so just to find my location, couldn't connect, etc. Several calls to AT&T, they couldn't help...
Now on the Note 4 the GPS seems to be ok! I am very happy about that.
So it looks like it was a phone issue, and has nothing to do with the service.
4)The battery saver and super saver modes are amazing. I love it so much. I put the phone on the super saver mode overnight, and when I woke up, not even one percent was used! That's crazy!
5)Fast charging is awesome.
6)Curved glass looks nice.
7)The metal edge design is cool. Although seems like it may be more prone to scratching.
8)The little audio jack on top where you plug in your headphones is very prone to scratching. This is because it is not metal like it was on the Note 3 - it's actually drilled right into the body, and the connector is inside! After several times connecting the headphones and taking them out, the minor damage to paint coating is visible upon close inspection. Annoying, but not a huge issue. Looks like the plastic edges did have their merits after all.
9)Camera is definitely somewhat better. I like the better face focusing and there is difference in clarity and performance in many situations. I was just at a birthday party a few days ago, and my phone absolutely wiped the floor with other people's iPhones when we all took pictures. My pictures were consistently better and clearer in a dark restaurant setting. Even my dad's iPhone 6+ ain't got nothing on my Note 4. It is certainly good, yes, but isn't quite as good as my Sammy.
So in the end, lets consider this... I'll sell my Note 3 for around $350 at best... I bought my Note 4 for $600. That's a $250 difference... Are all the upgrades worth a whopping $250? Definitely not.
I upgraded because I gave in to the hype, and because I wanted to see if the GPS would finally work, and if sound quality would be better. I think it was worth it for me because the GPS works, but if your Note 3 is overall performing ok, I really cant recommend upgrading if you have any sense at all or unless you manage to upgrade for much less than $250.