My main issue with the iPad 3rd Generation is that I own the 32GB model and it is constantly out of memory. Just to install iOS 8, I had to delete a bunch of apps and magazines. This wasn't a new experience since I am constantly monitoring the amount of space I have left and periodically deleting apps like Zinio (magazine app) to get more space.
When the Original iPad Air was released last year, I was disappointed with it for one main reason....the lack of Touch ID. I keep my devices locked with a passcode and the idea of just using a fingerprint to open it, is very enticing. The 5S had Touch ID, but the iPad Air lacked it. I refused to update when I knew that feature was coming and I could just get by with my iPad 3 for a while.
This year, I updated my iPhone 4S to an iPhone 6 Plus. I LOVE the Touch ID. It just makes the experience so much better and the way they have integrated it into Password apps, purchases from the app store, and ApplePay have been awesome. The iPad Air 2 has Touch ID (although you can't use it for in store purchases) and it is a major reason I updated this year. If it was missing Touch ID again this year, chances are, I would have kept the iPad 3 for another year.
When I bought the iPad Air 2, I decided to get the 64GB model. I am guessing that doubling the memory from my last iPad will be enough? The fact that the new iPad has Touch ID and more memory was enough to make me want to update, but the features don't stop there.
The Air 2 has a much faster processor than the iPad 3. Unfortunately, the iPad 3's processor was always a bit underpowered. When Apple releases the 4th gen iPad a few months after I purchased the iPad 3, and it had twice the performance capability, I can't say I was too happy.
Within seconds of using the iPad Air 2, the speed difference is obvious. When I hear bloggers say that there is little reason to upgrade from an iPad 3, I wonder if they have ever used the two devices side by side? Yeah, if you could care less about having a better experience in every single way, then by all means, hold onto that iPad 3. If you enjoy reloading tabs in Safari, don't mind waiting for articles to come into focus in magazine apps, don't mind seeing the equivalent of a bouncing ball when trying to use Lightroom's mobile app, etc.. then by all means don't update. For me, these differences were substantial and dramatically increase my pleasure when using the new iPad (which is often).
The new iPad is also lighter and smaller than the iPad 3. I have never had a problem handling the weight of the iPad 3, but I do find the new iPad easier to handle. Many complain about "Apple's fetish for thinness", however, I can understand why they want thinner and lighter devices, especially with phones and tablets. These are usually handheld devices, so any difference in weight probably means you will use it for longer periods.
One of the possible trade offs for this lighter, thinner iPad is that it has a smaller battery that last year's iPad. It is still over the 10 hours of normal use that Apple has advertised, so I don't see it as a real issue. Engadget's battery tests have it worse than last year's iPad, but better than the iPad 3 (2012). Also, Engadget tested with a wifi+cellular iPad, which would probably provide worse results than the wifi version I purchased.
For me, I rarely need to charge my iPad 3 more than just plugging it in when I go to bed. In fact, unless they can increase the battery to 24 hours or more, I am going to continue plugging it in at night. While, I am sure there is a user somewhere that is pushing video for 10.5 hours without being anywhere near a charger, I just don't think many people will notice the difference between ~11.5 and ~14 hours of battery life. When Mossberg did his tests, they were dramatically different from Engadget (he shows a 90 minute difference between the Air and Air2).
I should also mention the resonance that you feel when using the speakers on the iPad. Personally, my hands can handle slight vibrations. I have lived with a powerful subwoofer for several years, so my entire house shakes when we watch certain movies. Also, I played PS3 games using a DualShock controller and lived to tell about it. For me, the resonance isn't an issue at all. I mainly listen to music using Airplay (I have several blog articles about it), so I don't use the speakers in the iPad very often.
To me, the decision to make the iPad lighter and thinner makes a lot of sense. A lighter iPad will be felt by everyone that uses it every time they use it and there is nothing you can add on later that will make it lighter. For iPad users that are camping or doing something that keeps them away from electricity all day, you can buy a $40 portable charger that you can plug it into, if necessary. It really makes much more sense to prioritize features by which features are noticed by the most people. Also, if you are really put off by resonance from the speakers, you can add Airplay, Bluetooth, or just wear headphones. Once again, nothing I can buy will make a heavy iPad feel lighter...well I could hire someone to hold it for me, but I doubt I could do that for $40 or less.
One other thing that is better this time around is the screen. As I mentioned, I updated my Original iPad to the iPad 3 when the screen was improved. Personally, I think the screen is one of the most important features on a tablet. The current "retina" resolution is great. However, according to Apple, they improved the screen without changing resolution:
"The displays on previous generations of iPad used three separate components. iPad Air 2 changes all that, combining those three layers into just one. This eliminates gaps between layers, along with the internal reﬂectance caused by those gaps. The result? Colors are richer, contrast is greater, and images are sharper and more vivid."
Also, Apple put an antireflective coating on the new iPad Air 2. I have a floor lamp behind my usual position on the couch (best seat in the house) and it reflects off the screen. However, when I compare the 3 with the Air 2, the difference is easy to see. The iPad 3 has blown out areas caused by the brightness. The Air 2 softens the light. If you use Lightoom, it is like pulling back the highlights to get rid of the "blinkies".
For me, the upgrade from the 32GB iPad 3 to the 64GB iPad Air 2 was worth it. To put it in computer terms, the difference is more noticeable that going from a spinning hard drive to SSD. For me, the iPad Air 2 is nearly perfect. The one thing I would add would be split screen multitasking, but I believe that is more of a firmware issue than an iPad Air 2 limitation.