Apple’s newest mobile operating system has arrived and it’s a good upgrade, chock-full of tons of new stuff.

First, a caveat. If you have anything older than iPhone 5, you’re out of luck. In other words, Apple does not support iOS 10 on phones like the iPhone 4 and iPhone 4s. This is Apple’s subtle (or maybe not so subtle) way of saying it’s time to move on. Of course, you can still run iOS 9 on the iPhone 4/4s, and that may be fine for many consumers.

Older iPads are also cut off. Anything older than the 4th gen iPad (the generation before the iPad Air) and iPad Mini 2 will not be supported. For the iPod Touch, it goes back to the sixth-gen Touch.

Here’s are highlights of some of iOS 10’s biggest changes.

Lock screen: The first thing I noticed when I upgraded my iPhone 6s Plus to iOS 10 was the look and behavior of the lock screen. You now only need to raise the phone to wake the lock screen. Plus, iOS 10 adds two new screens that you can swipe to access: the camera app and a screen that shows widgets such as reminders, calendar, battery life, and news. And you can change those widgets to your liking.

“It makes accessing information...faster,” Michael Cole, CEO and cofounder of Picniic, told Foxnews.com. “For Picniic on IOS 10, we can now show all the family's most relevant events and to-dos on the lock screen of the phone...without opening the phone,” he said about his app that helps families organize their lives.

Messaging: With the new messaging app in iOS 10, Apple is trying to make up some lost ground to Facebook Messenger, WhatsApp, and Snapchat. And there’s so much new stuff that it’s a bit overwhelming. But there’s a lot to like. You can now replace highlighted words with emojis, do handwritten messages, tap into new animated sticker packs, and use Invisible Ink (the person receiving the message swipes over it to reveal the message) or "slam" your message (to get the most attention).

Related:

There’s an App Store too for Messages that allows you to send song snippets, search for GIFs to send, and, of course, browse the store.

And you can make payments right in the message.

Unfortunately, some of the features are not easy to find. But you can start exploring by opening a message thread then tapping on the camera, heart, or app icons to the left of the text box.

Photos: The revamped photos app allows you to search by the people or things that appear in the photos. Apple does this by using machine-learning-- so-called "deep learning"-- algorithms that analyze the images. (Apple, to some extent, is playing catch-up to Google Photos.) For instance, when I searched “water,” I got photos of various places under the categories of “Water, Waterfronts, Waterfall, and Water Mill.” The first three were accurate descriptions of photos that fell into the respective categories but the last one missed -- it interpreted the round profile of a leafless tree in winter as a water mill. Overall, it was very impressive, though.

Siri: Apple’s digital assistant now allows voice commands in third-party apps. Get Uber to pick you up, send money via Square Cash, or message people in LinkedIn or Slack.

New lease on life for current and older iPhones: Installing iOS 10 has made me seriously question the need to upgrade to the iPhone 7. I typically upgrade every generation (I use a Verizon plan that allows you to do that without getting penalized), but my iPhone 6S Plus with iOS 10 feels like a new phone. For now, I’ll just say it makes an upgrade a lot harder to justify than before.