(Caution: If you are the sort of person that doesn't care for reading about another's experiences, skip to the very last paragraph for the sake of your sanity)
This is the first tablet I've owned. I decided to go in the direction of a tablet based upon my needs. I consider myself a very mobile person. As a college professor, much of my livelihood depends on research, reading, writing and responding to e-mails, etc. I also enjoy my fair share of leisure like anyone else (watching the occasional YouTube video, chatting on Facebook, taking an interesting picture, etc.).
My first smartphone venture was with the Motorola Cliq, which, while I loved the Android interface, turned out to be a disaster in terms of hardware (no updates for the longest time, updates came exclusively from Motorola's website after a year and was unannounced, keyboard stopped working, touch sensitivity was below average, screen hurt my eyes, and I'm sure there were some other issues if I wanted to sit here any longer to recollect). I should have known better since I have owned 4 Motorola phones prior to that one and each one has been a hardware nightmare and or design fail (the antenna on every version of the V60 I owned would break while the Rizr would get dust under the screen, the software lagged badly, and the home keys started to peel off). The short end of the story was that the one non-Motorola phone I had owned prior to my Galaxy S4G was the T-809. That phone lasted me almost 3 years with minimal issues and continued to do well after I had unlocked it and gave it away to my family members (my wife owned one as well). It was this experience that led me to try Samsung once more.
My first run with the S4G was a bit of a disappointment as I started to suffer from this issue where the screen would randomly sleep and could not be recovered while the phone would consistently vibrate on and off in this state. At first, I wrote it off as an aberrant incident, but it continued to happen (sometimes up to 4 times in the same day). I decided I would just deal with it for the time being until the data connection was permanently lost. Mind you, I am very careful with my electronics and had not damaged it in any way. Fortunately, T-Mobile replaced it for me with a brand new one (only because it was entirely out of stock; otherwise, it would have been a refurbished one) and I have had zero problems. I suppose that the lesson to be learned from this tidbit is that, for better or worse, products can be hit and miss.
The moral of this, admittedly lengthy story, however, is that the tablet will be only as good as the extent to which it meets your needs. For me, it is exactly what I was looking for. I became rather comfy with the Android interface from my use of smartphones and I enjoy Google's applications. When comparing the weight of this thing to my laptop, I've dropped 6 pounds from my carrying weight. Having to lug around a 15" laptop along with several books in a messenger bag takes a toll on the tension in your shoulders. Sure, I've used lighter laptops (11" and 12"), but unbelievably, even a couple of pounds makes all of the difference in the world for me. Since owning the tablet, I've turned my laptop on only a few times in the past week.
As for the tablet, like others have mentioned, it's new. As a new device, it will have its problems (which, if Samsung is to be a responsible manufacturer, they will iron out these out with time). This is why it is usually best, if you can, to wait and buy a device after it has been out for a couple of months or more (supposing that the manufacturer has actually tried to fix the issues with the initial runs). As for the software, I don't really experience too much lag on the home screen (it's hardly noticeable), but I do suffer from the awful keyboard lag on websites. I have patience and I'm hoping it will be fixed with the new update. Regardless, the majority of my experience has been overwhelmingly positive, but I am also not going to pretend it hasn't been without it's problems.
So... Does it have its drawbacks? Sure. Is it perfect? Absolutely not. Ought it to be for a $500 device? Maybe; maybe not. We can debate the merits of that over a cup of coffee some time. Is it perfect for you and your needs? In my case, yes.