This is the year the iPad line has reached significant, noteworthy maturity. It’s worthy of a milestone.

The iPad Air is to the original iPad what the iPhone 4 was to the original iPhone.

The iPhone 4 was the model where all the foundational components — the screen, the hardware design, the camera, the processor — came together just right to make an iPhone without compromise.

The original iPhone compromised on a lot of things: it had a lousy camera and only worked on AT&T’s EDGE network.

The iPhone 3G and 3GS compromised on their hardware design — using a plastic casing to allow better cellular reception and battery life.

The iPhone 4 left those compromises behind while also upping the ante. It had a beautiful design of glass and steel while keeping the fast (3G) cellular data and good battery life. Additionally, the iPhone 4 added a significantly better camera and, of course, the introduction of the Retina display.

Similarly, I think the iPad Air is “finally” a full-sized iPad without compromises. It has a gorgeous display, excellent battery life, it’s powerful, and, of course, it’s very lightweight and easy to hold.

The iPad Air (and Retina iPad mini) mark the end of one chapter and the beginning of the next for the iPad line. And so, now that we’re here, where does the iPad lineup go next?