If you liked last year's iPad Air, you'll almost certainly like this year's version, unveiled early last month (along with the 5K Retina iMac) by Apple CEO Tim Cook. The iPad Air 2 features Touch ID, a (much) faster system architecture and an aluminum enclosure that is both thinner and lighter than the first-generation iPad Air it replaces.As with previous lines, the iPad Air 2 comes as both Wi-Fi and Wi-Fi/cellular models. The Wi-Fi-only devices cost $499 for 16GB of storage, $599 for 64GB and $699 for 128GB. The cellular/GPS iPads cost $130 more at the same storage tiers. Supported carriers include Sprint, AT&T, Verizon and T-Mobile in the U.S.I've spent the past week or so with a Space Gray 128GB cellular/GPS-equipped iPad Air 2. Even though it looks similar to last year's model, it offers significant improvements.Now with Touch IDThe star feature is the Touch ID sensor, which has been included in the iPhone lineup since 2013's iPhone 5S, and is now available on the iPad Air 2.With Touch ID built into the Home button, you can log in, make purchases and authenticate third-party apps with your fingerprint. Apple insists that fingerprint data is never transmitted or stored on iCloud servers; your encrypted fingerprint data never leaves the device's secure enclave. If an app or service requires Touch ID authentication, the requestor merely receives a yay or a nay regarding a fingerprint match.Touch ID supports five fingerprints that you can, if you want, assign to several people. However, that simply enables them to access the tablet; unfortunately, they don't have their own logins or profiles.Also, be aware that, although it has Touch ID, the iPad 2 does not have built-in NFC and so can't use Apple Pay to make payments in retail locations the way the new iPhone can. (You can, however, use Apple Pay for in-app and online purchases.)Now that Touch ID is available, I recommend upping security standards for anyone who purchases this iPad (or iPhone models with the Touch ID feature) so that simple, four-digit numeric passcodes are replaced with a more complicated (and harder to guess) passphrase. (To turn off Simple Pass code, check for the option under Settings: Touch ID & Passcode.) With Touch ID supported, you will hardly ever have to enter the longer password -- with the exception being immediately after a restart (to help thwart hacking attempts).Lighter is betterWhenever I review iPads, comfort is always a top consideration. To that end, the unit's weight and how it feels in hand -- especially during a long session -- has always played a big factor in my recommendations.When given options, I've always used the lightest device available. For example, in my experience with previous iPads, I usually chose the iPad 2 over the iPad 3 with Retina display, mostly due to size and weight. After long reading or gaming sessions, I felt less wrist strain with the lighter iPad 2, even though the iPad 3 has the better display. However, once the iPad Air was released, I happily updated. In the same way, the new iPad Air 2 retains the features that made last year's iPad Air great and adds more features while being thinner and lighter.The iPad Air 2 is still based on the chamfered-edged aluminum unibody enclosure, measuring 9.4-in. high and 6.6-in. wide, the same as its predecessor; however, at 0.24 in., it's slightly thinner. Even so, the iPad's frame is still rigid and obviously solidly built. One thing I noticed, though: If you hold the tablet and exert force on the edges, the iPad Air 2 is more perceptible to LCD screen distortions at lower stress points than previous models.As well as being thinner, the new iPads are lighter, weighing .96 lb. for the Wi-Fi model and .98 lb. for the Air with cellular/ GPS capabilities.The 9.7-in. display has a resolution of 2048 x 1536; that's 3.1 million pixels at 264 pixels per inch. Despite having the same resolution as last year's model, the display has been completely redesigned. It combines the touch sensor, LCD and cover glass into one layer, eliminating some of the spacing found in previous generations that helped cause reflections. The iPad Air 2 also features a custom-designed antireflective coating, further reducing glare and reflections by up to 56%, according to Apple.In real-world testing, I did notice improvements -- reflections weren't as detailed or bright when I compared it side-by-side to last year's iPad Air -- but this still isn't a device you would want to use in direct sunlight. (The new iPhones handle sunlight better than the iPads do.)Like the iPhones, the iPad Air 2 comes in three familiar colors: Space Gray with black display borders, Silver with white display borders and a new Gold/White option. On the right edge, the mute/rotation lock switch has been removed, leaving just the volume up and down. The sleep/wake button is still on the upper right, at the top of the tablet.Increased performanceThe iPad Air 2 marks the second generation of iPads to carry a custom Apple-designed 64-bit chipset, this time called the A8X. The A8X features 3 billion transistors, resulting in up to 40% faster processor performance compared to the A7 in last year's iPad Air, and two-and-a-half times the graphics performance.Like the new iPhones, the iPad is also equipped with a new M8 coprocessor, which tracks gyroscope, accelerometer, GPS, compass and barometer data without taxing the main processor.In my tests, apps launched faster, webpages displayed faster and apps like Action Movie FX rendered videos faster than on last year's iPad Air. At this point, we're talking a savings of seconds for most operations, but the performance improvements are, indeed, there. Primate Labs, for example, benchmarked it against other Apple products and the iPad Air 2 came out on top.The iPad Air 2 supports Bluetooth 4.0 LE and dual channel (2.4GHz and 5GHz) 802.11a/b/g/n/ac Wi-Fi, including support for HT80 with MIMO, which delivers better bandwidth for faster uploads and downloads over wireless.Improved camerasApple has also updated the iPad's cameras. The iSight camera at the rear of the tablet now uses an 8-megapixel sensor, capable of shooting 3264 x 2448 photos and 1080p video. It's also capable of time-lapse photography, 10-photos-per-second burst-mode, 120fps slow motion, and a panorama mode capable of taking photos up to 43MP. The camera app offers a built-in timer and on-the-fly exposure control.The front-facing FaceTime camera is also improved, with an ƒ/2.2 aperture that, according to Apple, lets in 81% more light than before. The 1.2-megapixel camera also shoots video at 720p, while dual microphones working in concert with noise-reduction technology to help capture sound, automatically switching focus based on whether you're using the front or rear camera.Despite the updates and changes to the iPad Air 2, battery life is remarkably similar. Apple estimates you'll be able to get nine to ten hours of use out of it, but I've found Apple's estimates to be, if anything, pessimistic. In my on-and-off daily use -- the way most people use an iPad -- I found it could go two or three days before needing a charge.Bottom lineWhen the iPad was first released in 2010, I described it as a leap ahead for computing -- a tool that simplified interaction in a way that I thought would make computing accessible to even more people. And when I looked at last year's iPad Air, I said the only thing that stopped me from calling the Air the ultimate personal computer was the lack of Touch ID support.Well, this year's iPad Air has the TouchID sensor, the fastest mobile architecture on any platform to date, an improved camera subsystem, more memory and storage, and comes in a thinner, lighter enclosure. With the media and content in the App and iTunes Store, free educational content from iTunes University, regular feature-improving software updates from Apple, and the simplicity and security inherent to the Apple ecosystem, the iPad Air 2 is an absolute no-brainer for anyone looking for a tablet.The iPad Air 2 is, without hyperbole, the best tablet on the market.