I took advantage of the various offers that Best Buy had to trade in my iPad Air for the Air 2 for a fairly reasonable out of pocket expense.
Thoughts so far are mixed. I use my iPad very heavily every day, primarily for web browsing, email, music, magazines, note taking and writing, etc. The difference in thickness is quite noticeable to me, but it's not earth-shattering. It definitely makes it just that much easier to hold one-handed though which I appreciate.
The screen is nicer, but not so much so that I would pay for it alone. I think the screen on both devices is very good. I have not had it for long enough to make a definitive statement about the battery, but so far it definitely seems to be draining noticeably faster than on the original Air. It's not a deal breaker, but the Air's battery was by far the best battery life I'd ever seen. Even with my heavy daily use I averaged between 14-20 hours and 5-7 days of standby. I basically charged it once every 5-7 days. I suspect the Air 2 is going to get me more like 12-13 hours and 3-4 days of standby.
The speaker vibration was something I ignored before, and there were no display models out to test it, and I'm surprised at how noticeable it is. I can see that it could really be irritating to people who use the speakers a lot. Fortunately I rarely use them while holding the device, so while it's not perfect, I can live with it.
As for the performance, I'm actually quite surprised at what a jump this is. From a pure speed standpoint, everything happens just that little bit faster, but it's enough that you constantly notice it. Programs open and switch faster. There is less delay when you switch to a program and quickly try to activate a control, for example. Web pages seem to jump onto the screen instantaneously - even in Mercury browser which is not yet using the newly accessible rendering engine. So far in the day I've been using it I haven't seen any browser refreshes and many other programs stay open and active as well making switching between them that much more seamless. This really speaks to how much better the experience will be once Apple modifies the underlying code to treat programs more like a real computer where even if the contents get dumped from RAM they can at least be held in a page file.
Overall, I'm mixed in my opinion. I think that for light users and especially those that appreciate good battery life, the original Air is where the value is now. There is something to be said for a device that can live so much of its life far from a plug. On the other hand, if you are a heavy user and appreciate speed, the Air 2 is undoubtedly faster and more fluid to use.