Our April 2011 iPad 2 is still the main tablet in our house, but will be picking up an Air for Christmas.
Always thought the 3 and 4 were compromises that shouldn't have had to be made - I don't want my tablet thicker and heavier, I want it more portable! The Air, in my opinion, is the first true successor to the iPad 2. That fact that the 2's also still being sold is a testament to its great design.
Even at almost three years old, it still runs the vast majority of the latest apps very well. Sure, Safari crashes sometimes, but at the end of the day, for how long it's lasted, it's great value for money.