Bottom line, if you have an iPad 4 or older or an original mini, you'll love the improvements in the iPad Air 2. If you already have the Air, then you may not feel the improvements are worth spending hundreds of dollars for and may be happier waiting for the Air 3 or whatever Apple brings us next.
Thinner and lighter than any previous full-sized iPad; Improved camera; NFC chip lets you use Apple Pay for online purchases; Faster than previous iPads; Better sound than previous iPads; Thumbprint reader for increased security and for use with Apple Pay
Incremental updates may not seem worth the purchase to people with the iPad Air