When Apple finds a formula it likes, it sticks with it. So the outer design of the iPad mini hasn't changed in any appreciable way since it was first introduced in 2012. The iPad mini 3 is still an excellently built tablet with a metal back case and a 4:3 display. It's still a bit too wide to hold in one hand, but much more portable than the iPad Air, with bezels around the screen that are just a little larger than is ideal.
The iPad mini 3 is thus not much of a change. Apple has added TouchID and an alternate gold color option and... not much else. The camera, processor, and everything else inside the device is exactly the same as last year's model. The iPad mini 3 got maybe a grand total of four minutes of stage time at Apple's event today, and it was not demo'd at all. It starts at $399, which seems like a pretty steep price to pay for TouchID — especially when last year's model is still available for $100 less.
If you are already using it on your iPhone, not having TouchID on your iPad makes things feel just a little off. Even though it's generally easier and faster to type in passwords on an iPad than on an iPhone, you get used to just resting your finger on the Home button instead. It's a nice inclusion.
The iPad mini 3 is quite possibly the best small tablet on the market today. But it doesn't feel like it's from the future. It's a little thicker and heavier than you'd ideally like a small tablet to be, and it's frustrating to have the speakers at the bottom of the tablet. I expect it will feel overdue for a design refresh next year.
And if you're one of the crazy ones who just bought an iPhone 6 Plus, it's pretty tough to justify buying the iPad mini 3. The two devices are simply too close in their size and functionality, and if you want an iPad you should step up to the Air.