One big change on the iPhone 5S was the fact it arrived with iOS 7. This was clearly the flagship device for the new operating system, and it showed off the UI redesign superbly.
Now we're all the way up to iOS 9 and beyond, bringing a few new refinements and extra features, without really altering the aesthetic established by iOS 7.
Right now, the latest iPhone 5S software rests at iOS 9.1, with the recent addition of new emojis. The Health app is now here, and the HealthKit framework, offering the chance to track your fitness and health (and even your caffeine intake) as well as connect to more devices within the home.
It also finally opens up things like the keyboard, which means you'll be able to customise your phone in
ways you couldn't before.
Unfortunately Apple Pay, a new way of paying for goods and services in store and online, is not going to work on the iPhone 5S because it lacks NFC, but pair with a new Apple Watch and you're laughing all the way to the bank (until you see your balance anyway).
For those that missed the iOS 7 update, you'd best gird your loins if you're not a fan of colour all over the place. iOS 7 is a lot brighter, cleaner and sleeker than its bloated predecessor, but it does look like Jony Ive has dipped into his crayon pot a few times. But don't think this is a negative: I like it.
The colours on offer are fun, fresh and most importantly distinctive, giving a real unique feel to iOS 7, iOS 8 and iOS 9 that other platforms might not have. Photos, Safari and Music are all changed, as well as a host of other apps too, and while some have labelled them 'childish', they're clearly indicative of the new style Apple is looking to create.
And when iOS 7.1 landed, things were tidied up a bit and helped appease some Apple fans looking to not feel like they've fallen into a big bag of rainbows.
What I do find frustrating in iOS is the dependence it has on the settings menu, with various app controls all housed here instead of within the apps themselves.
It's annoying if you're in the Facebook app for example and want to adjust the notification settings. You have to exit the app and navigate to the setting menu instead.
Look beyond the UI though and you'll see that the iPhone 5S is much easier to use than the phones that came before it, which is impressive for a phone that was already market-leading in its simplicity. The software is almost identical to that running on the iPhone 6 and iPhone 6 Plus.
Dragging upwards from pretty much anywhere on the phone will open the Control Center, giving access to the music player, brightness, quick apps such as a timer, torch and calculator, as well as allowing you to switch on and off elements like the Wi-Fi and Bluetooth.
Yes, it's a notion that's been part of Android for a number of years, but it's been done in a way that feels a lot more solid and intuitive, never changing with notifications so you can easily trust that when you need a torch you can get to it easily.
That said, the torch was an odd area of the Control Center. Whenever lifting up the tab to access said function, you'd always need to wait a second or two before being able to hit any of the quick app icons. It's not a huge problem, but one that quickly got tiring. It's like the whole drawer needs a second to boot up.
I also found an odd glitch here too: the music controls don't work over Bluetooth headphones, nor on the lock screen. This was fixed with a reboot, and hasn't happened for a while, but it didn't give me massive confidence in the device.
There's also a new notification area that can be accessed by dragging downwards. Thankfully unlike the Control Center, this can be customised: you don't need to have to look at stocks or your upcoming meetings or lack of social engagements if you don't want to, but there's always information on the weather there, which is nice when you realise you'll need a coat.
This is also the place where you'll get any missed notifications, be it a call, message or that jacket on eBay you were looking to buy when someone's outbid you on it.
It was a bit of a wasteland, but Apple has changed that with the iOS 8 (and iOS 9) update, adding more intuitive interactions, and live widgets that update with key information - plus the ability to directly reply to messages there too.
Both of these areas are nicely designed too, with translucency that allows you to see very vaguely through to the rest of the phone. This gives the whole handset an air of completeness. It feels like a phone that's able to connect within itself and not fall apart when a new app rolls into town.
Since iOS 7.1 the phone and messaging buttons have been toned down in colour somewhat, meaning less neon green and a more pleasing look to the eye.
Multi-tasking was also given an overhaul with iOS 7 too: gone is the bar that appeared at the bottom of the display when you double tap the home button.
The double tap action now sees the screen you're viewing minimised to a thumbnail in the centre of the screen, and a horizontal list to the right of it made up of small panels of all the other apps running in the background.
The relevant app icon sits beneath each screenshot and above them you'll find your most recently used contacts, making this a quick stop shortcut screen for apps or contacts.
The layout reminds me of the multitasking menu on HTC's Sense UI, and you can scroll through the various applications, swiping up over thumbnails to close certain applications.
I'm not overly keen on this new design as the interface does break things up when flicking between apps. (On the iPad you've got the great four finger swipe to move between open apps – could this have not been repeated on the iPhone?)
There's obviously some other new features, as well as some old favourites.
For instance, a long press on any app will engage the editing mode for the home screen, meaning you can uninstall anything you fancy (as long as it's not hard-coded by Apple) and drag and drop it onto another icon to make a folder.
The folder system and organisation method was a great idea from Apple, and it was improved with iOS 7, allowing users to dump more in one folder and just swipe through it to see more apps.
It's not a big thing, but show it to any iPhone user now and they'll smile at such an important fix. Who wants 'Games 4' anyway?
The rest of the phone's interface is mostly a cosmetic upgrade - there are some important performance tweaks, such as on the internet browser and camera UI.
But iOS is really a lick of exceptionally powerful and much-needed paint, keeping the raw power and integration that Apple prides itself on while taking some of the clever ideas from other smartphones on the market and making them its own.
iOS 7.1 update
There are a few extra features that I need to mention here to show that Apple has been through and had a think about how things work with the new iteration of iOS 7.1
First, the parallax effect has been given a little bit more respect within the OS, with the ability to turn it off when your first turn on the wallpaper making things a lot more fluid and understandable to people.
It's not locked down in the Accessibility menu any more either, rather when you set the wallpaper instead.
The menus themselves have been given something of an overhaul too, thanks to the ability to mark out where the buttons are.
This is a weird one, as it's not a problem I'd come across really. Apparently swathes of you were worried about not being able to tell what's text and what's a button thanks to the large white expanses being thrown around the screen where usually things used to look like buttons.
Well, now you can do just that once more, as a setting in the Accessibility menu will let you swoop in and make every button look a little bit uglier thanks to a tab sitting around it, or words in a list will be underlined if you can tap them.
The extra navigation in iOS 7.1 also included a nifty feature that lets you choose to be able to select menu items and move around the screen using a tilt of the head.
Some have likened this to the Smart Scroll feature in Samsung's Galaxy S4, but in reality it's designed for those unable to interact with an iPhone using their hands, allowing them to control the interface using head gestures and pre-determined times to wait to select menu items.
And finally: a hurrah for the fact that the calendar was re-enabled with a split screen view thanks to a toggle at the top. Apple dropped this for the iOS 7 update to its devices, but now you can be in the month view and still see what appointments exist on any given day you tap.
You know, like every other smartphone ever.
iOS 8.1 update
You can find out the full details of what the latest version delivered in our iOS 8 review. There have been a few menu tweaks, third-party extensions for Touch ID and keyboards, some extras for the camera, the ability to share your location with contacts, and more integration with Mac.
In iOS 8.1 Apple relented and brought back the Camera Roll. As we've mentioned there's also a new Health app to help you keep an eye on your fitness, but again don't expect this update to switch on Apple Pay for the iPhone 5S - the Touch ID-enabled digital wallet remains exclusive to the NFC-touting iPhone 6 and iPhone 6 Plus.
iOS 9 update
We're all the way up to iOS 9 now, or more specifically iOS 9.1. The highlights include improvements to Apple Maps, which now has public transport information in certain locations, plus an overhaul to Siri's functionality.
Apple's personal assistant is now proactive, being able to make suggestions of its own, such as appointments you might want to add to your calendar.
There's also a new News app, which works a bit like Flipboard, giving you a personalised feed of sources and stories you might be interested in. Plus iOS 9 improves the efficiency of devices and tweaks the keyboard to, among other things, make it easier to tell whether caps lock is on or not.