I'm privaledged enough to have a couple of iOS devices laying around that I don't use daily and also fortunate to be a registered Apple developer, so I've been able to use iOS 9 since early June. Most of the changes are relatively minor - this isn't an iOS 7-level redesign here, but several things have been reworked to allow you to get more done on your devices. So as a minister, here are some things that I care about and I think you will too.
New system font. This may seem like something you wouldn't care about, but once you see it, it will be hard to unsee it. The new font is named San Francisco and was custom-designed by Apple themselves. And it's marvelous. To me, it's much better for reading, and apps like Instapaper and Twitteriffic (where I spend most of my time reading) have been updated to support the new system font. Text is much more legible by the glance, and this font was pioneered by none other that the Apple Watch. So it was made for high-resolution but smaller screens.
Multi-tasking is much faster. If you're like me, you're flipping between different apps on your iPhone or iPad all the time. Instead of the one-card-at-a-time approach like in iOS 8, iOS 9 features a stacked card layout to the left. Flipping between apps and quitting them is much faster.
Safari View Controller. SVC is a term used by developers to describe a new way that iOS handles web views, i.e. when you click on a link inside of another app. Say you're browsing your Twitter feed in the Twitter app and you click on a link that brings it up in the in-app browser, which means you don't leave the app you're using to view web content. Now apps can use Safari View Controller, which means everything is based on (Webkit) Safari for web browsing. Using SVC in Twitteriffic, which adapted SVC about a month ago in their app, has significantly sped up load times for websites.
Ad blockers. Speaking of Safari, iOS now allows you to install ad blocking apps. Just today, Overcast and Instapaper developer Marco Arment released his ad blocker called Peace, which connects to Safari (enabled after you buy the app in Settings > Safari > Content Blockers) and blocks almost all incoming ads and tracking using Ghostery as a backend. With 300 million+ iOS devices out there, ad blocking is going to become a big deal here in the near future.
Great iPad-only productivity improvements. While some features are only available on newer iPads (iPad Air 2, iPad Pro, and iPad Mini 4), the productivity improvments are awesome. For example, I'm writing this very post on my iPad Air 2 using Slideover to check and research certain websites as I write, while never leaving Editorial, my main writing app. Slideover lets you bring in certain apps that support it from the right side of your screen. Split View lets you run two apps side by side. This is a powerful feature and only available on the aforementioned models, but it's great to work side-by-side in the new Notes app and copy text directly from Safari into my document. A great tool for preachers writing sermons for sure. There's also picture-in-picture now - whatever video app supports it, you can have a video in a box overlaying your screen in virtually any app while you're surfing the web or writing a post.
Search is getting better and better. Swipe to the left on any iOS 9 device and you'll get a nice search screen. This goes deep too - apps can enable this quick search to search within their apps as well. For example, I use Scanbot to make scans of important documents and file them away in Dropbox. Now Scanbot will let me search with its documents with the quick search. One swipe, type, and I'm there. It's very nice and very quick.
Battery life and low power mode. If you're like me, you're always running on empty with your iOS device battery. iOS will have improvements with battery life and Apple has reported that newer devices may see 1-2 hours more life with iOS 9 because "there's switches that we can switch that you don't even know about." One of the benefits of making the software and hardware, I guess. One other major improvemnet is Low Power Mode. Every time your device gets below 20%, it will ask you if you'd like to go into low power mode. Apple has implemented this really intelligently. Things like not lighting the screen up for a notification if the phone knows its laying face-down on a table or in your pocket can save you a few precious minutes of battery life.
New Notes app. Last but not least is the new Notes app. I never had a use for Notes - the syncing was always unreliable and it didn't have enough formatting featuyres for me - but that's all changed. Notes can now have bulleted lists, photos, sketchings, as well as formatted text. The syncing engine is now built on Cloudkit, so most of the syncing problems are history. Apple says that 80% of users use the Notes app, which isn't very surprisng to me. So if you're a Notes user, you're in for a treat. They've also redesigned the Mac app as well on El Capitan, so when that releases on September 30, you can use it with your Mac as well.
iOS 9 won't appear to be a huge change on the surface to the average user, but sublte improvements in infastructure and stability will make this a great iOS release. Coming from using the betas for two months and now the actual 9.0 release, I can say that the update process was painless and easy and the OS seems incredibly stable.
If Apple continues this trend with toning down the number of major feature updates and including some great maintenince updates like these, I think iOS is on a very good track.