I have the Air and Air 2, after 15 months with the Air and just got the Air 2 couple of weeks ago. My sister has the iPad 4 and I think it's still good for web browsing, you tube and most simple games.
Problem is, try running XCOM, Modern Combat 4, The Wolf Among Us, Tales from the Borderlands or Hearthstone on it. The original Air is fine for all of those, but the iPad 4 shows really bad frame rate. Most people I know would never play most of those games on an iPad having a PC, but I do, so...
The iPad Air 2 is a monster, but the original air still runs everything with great performance, the reason I got it was because I had the money and liked the feeling of its screen, more solid, less plastic, and the laminated display gives a really good sensation when using it. Overall, my Air is still great and my sister don't even notice the difference btw it and her iPad 4, reason she'll probably keep it for another year or two.
My cousin still has the iPad 2 and is very pleased with it (of course he misses the retina display) but for what he does, he says it's fine. I have friends satisfied with their first generation iPad mini. In the end it all comes up with the need for a stronger GPU and gaming, cause internet browsing, you tube, facebook and some angry birds and Worms is perfectly on most iPads. In the end, it all comes down to the retina display.