I went from a 1st gen iPad 64gb/3g to the iPad3 64gb/4G My wife wanted my iPad 1 so we needed another anyway. She was always on it, and I often had to prise it from her when I needed it...lol Otherwise I may not have bothered upgrading for a while. I think the upgrade from the 1 to the 3 is maybe worthwhile, though if one already has a gen 1 and especially if you have a iPad2 I certainly would'nt say the iPad 3 is a must have, as the earlier iPads are still very good, even the iPad1 is still a pretty effective and useful device to own.
One of the main differences I noticed quickly, was how much quicker web pages load over the iPad1, the screen which has already been covered numerious times in other threads is obviously better, more detailed, sharper text, which is better for browsing and reading books etc. But the original iPads screens were'nt that bad anyway, they were actually pretty good and still are!. Sound is a little better too when compared to the iPad 1, though about the same as the ipad2 which is to be expected.
I think the new screen is good and obviously better, but not a big 'WOW.. gotta have one of them feeling.. I think I would have been more excited if Apple had used Samsungs new Super-Oled technology, as I've no doubt that's the directon that most panels will go in the future, currently its all a matter of cost. For example I have a iPhone 4S and the wife uses a Samsung Galaxy S2 phone, and though the S2 has slightly lower resolution it's display is noticable better than my iphone4s, and of course they don't need any backlighting at all, so blacks/colours looks superb.
Just hope I live long enough to see them introduced widely on TV's I can afford...lol
My son has a 64gb iPad 2 and we have compared them, and though he says the screen is better especially on text, he reckons he cannot see too much difference on video's/films, though he did admit a blu-ray film I had ripped and installed did look noticable better, but he did say he is not bothering to upgrade again for a while, as he did'nt feel the need.
I was also hoping Apple would have increased the max memory to 128GB too, so a little disappointed they didn't.