Let's start with the skin, shall we? KitKat 4.4 is very pretty. So what, you say: JellyBean was pretty (the first iteration of Android to be able to make that claim for itself without blushing). You'd expect its successor to be easy on the eyes, especially when it has been so long in the making.

But while KitKat 4.4 may not represent the same canyon leap in interface design as iOS6 to iOS7, it is a fairly dramatic overhaul. 

Throughout the OS, the design has fallen away, leaving the content to come to the fore (is this ringing any bells, Apple fans?). The blue hinting that defined stock Android has been ousted in favour a slightly off white (in fact, much of KitKat is now monochromatic). It shares a minimalist meme with iOS7 - anything between you and the words, pictures, videos or animations is Evil.

The newly-whitened menu bar icons are the most ever-present example, but it runs throughout the Settings and widget selection screens.

KitKat's graphic polish should raise a few alarms in Apple's design studios. For example, study that new Camera app icon for a moment on the Nexus 5's stunning 445 ppi screen. It's so well finished that you wonder how the design team justified the months spent polishing it, right down to the subtly shaded shutter button. It shows where Android's Holo design movement is heading, and we like it.

And here's the bit where we explain why KitKat 4.4 is so remarkable. As you probably know, Google Now - the company's personalised, predictive search service - has been steadily improving in functionality: every month or so, it gains another feature that tries to intelligently predict what you need to do next (and it taps into everything - from your location to your recent searches to your email).

With the launch of KitKat, Google has effectively reversed the Android experience into Google Now. 

The screens you look at when you use the phone are all extensions of Now (whereas in the past, Now was the bolt-on), and search has been integrated into every aspect of the phone's use in a way that makes rivals look Old. 

As the team  revealed, most of the files that previously existed in Android's launcher (GoogleHome.apk) has been shovelled into the Google Search app - the launcher is now a shell that won't launch. 

You'll be ahead of us in realising the far reaching implications of this: in theory, the Google Search app you download from the Play Store can transform any Android handset (hello, Samsung and HTC...) into the full KitKat experience.

When you first launch 4.4, you'll find Google Now permanently fixed to the left of your home screen. You can turn it off in Settings, but you'll be neutering the phone's capabilities. 

Take the dialler. Diallers make calls: they show contacts, and have numbers you tap. They've done this for years. But with KitKat 4.4, the dialler is now also a search engine. 

Try typing 'pizza', and look at the results. Yes, there's the entry for 'Pizza Hut' around the corner that you manually saved a few months back. But now there are also entries for the three other local pizza places. Then get an unsolicited call from another local pizza place - go back to your call history, and notice that Google has recognised the number, and added the Caller ID details. Pick up that iPhone 5s lying around the house, and try the same trick. Android 1, iOS 0.

Elsewhere, widget and home screen obsessives will instantly fall in love with KitKat 4.4: you can create as many screens as you like. Yes, we know, we sobbed gently at the news, too. However, we'll admit to struggling to work out how to create new screens in the first hours with the OS (Google's usually faultless at including overlay tips when first using a stock Android device - not in this case). 

For the record, it couldn't be more straightforward - hold an app in the drawer, drag it to the right of the last existing home screen, and a new one is created. If you want to get rid of a screen, just drag all of the icons off (there should really be a way to delete an entire screen at a swipe, but maybe that's in the next release).

You'll also notice that the widget drawer has upped and moved home: instead of living in the App Drawer, it's now a prod of a screen away, alongside the wallpaper selector. It's a design that's reminiscent of HTC's Sense 5 (and now we come to think of it, the positioning of Now next to the main home screen isn't that far removed from HTC's Blinkfeed philosophy).

Lastly, Google has burned the midnight candle in attempts to make Android leaner - to the point where they claim that KitKat will run on a device with as little as 512MB of RAM. We have no way of testing the claim, of course, but it's good news for owners of older handsets.

Say 'OK, Google' to KitKat, and it will act. At least, it will if you're in the USA. The cool voice activation function first debuted with the US-only Moto X is baked right into KitKat 4.4. But if you launch the OS in the India, you'll wonder if your phone is broken. Say 'OK, Google', and nothing happens (Android forums are currently packed with Brits factory resetting their Nexus 5s, in the hope that it'll bring the feature to life).

There is a way round it, you'll be jolly pleased to hear. You just go into Google Now settings, and switch to 'US English'. Wait a second or two, and the 'Speak now' help tip appears in the search bar - voila.

Quite why the feature is set to Off for Indian users is beyond us. And bafflingly, the Nexus 5 advertising promos for the Nexus 5 on this side of the water mention the feature.

But enough grumbling - does the voice activation work? Yes. It's awesome, in fact. So good that a week with KitKat changes everyday habits. Shouting 'OK, Google' in public didn't get any less weird as time went by, but when you're either out of earshot or alone, giving the command followed by 'Text Lady GaGa, What the hell is that new album about?' is perfectly natural. 

Opening Hangouts and typing away on the keyboard feels Old after only a few days. And 90% of the time, the voice recognition is accurate - even with our painfully plummy English accents and Google Now set to US English. It's reason enough all by itself for upgrading to KitKat, or rushing out to buy a Nexus 5.

Just about every Google app in KitKat gets a point release update, although we'll wager that you only notice the difference in four of the apps - Play Books, Quickoffice, Gallery and Hangouts.

The Play Books app is the showcase for KitKat's new 'immersive' mode - a pretentious way of saying that the content fills the whole screen, displacing the menu bars top and bottom (you can get them back if you need navigation, simply by tapping the screen). 'Immersive' is simple but effective - we can't wait for the World Of Third Party apps to begin exploiting the feature, especially readers such as Flipboard and Feedly.

Quickoffice has been upgraded, with the aim of seducing Microsoft Office fans into the Android fold (and the threat to Microsoft runs deep: every KitKat device in future will come with Quickoffice, making you question why you'd need to buy the Office suite). 

Not only can you open Word, Excel and PowerPoint files with the app, but you can also create them. Further, the app is tightly integrated with Google Drive, your device's local file system and cloud services. It may not be glamorous, but it's powerful and it works. 

However, it's the changes in the Hangouts app that really steal the headlines. Google has now added SMS to the chat and video calling client, and given you the option in Settings of choosing it as the default for text messaging. 

It works well, although you may need to concentrate: we run two Gmail accounts (work and home), and tied ourselves in knots in the first few days, with messages popping into the less-used account. We eventually discovered that you can switch the profile associated with text messages in Settings.

The Gallery app on first acquaintance is identical to its predecessor - until you go to edit an image. Up pops an advanced photo editor that's deceptively simple in design, but awesomely powerful in use. You can crop in seconds, pick any one of dozens of filters and effects and change the exposure in moments.

Your phone will become your credit card. Promise. In America, they have a thing called Google Wallet.

It's an app that lets you pay for stuff, using the handset's NFC chip. Back here in ancient Britain, with our lack of electricity and absence of wheels and fire, we have no such marvels. Undeterred, Google has built Tap and Pay into KitKat's settings screen. Only now, without Wallet available in the India, it's an interesting empty space with a 'Learn more' button. One day; one day.

Google Now relies on knowing what you're doing, and where you're doing it. So it's no surprise that KitKat has a lot of location settings, and most of them would like to be left on, thank you. 

Aside from the privacy issues, they also raise another, more practical problem: location services eat batteries. 

So it's good news that KitKat marks a revamp of the Location Settings screen, with clear indications of which services are calling on your location and how much power they're consuming. You can also quickly switch between three location modes - High accuracy (GPS and wifi), Battery saving (wifi and mobile networks) and Device accuracy (GPS).

There's a chance that after a month or two of living with it, we may end up feeling much the same way about KitKat 4.4 as we have iOS7. For all of their party tricks, design flourishes and architectural overhauls, neither OS redefines how a mobile operating system works.

But while that may be true, it's KitKat that comes closest to moving the game on. It's clear what Google is aiming for - a system that knows you intimately, and is smart enough to predict your next whim (or tell you what it should be...). KitKat is all about Google Now, and it's a gamble that pays off.

We'd stick by our view that for tablets, iOS7 is the superior life form (helped no end by an app arsenal to die for). But for now, at least, KitKat 4.4 is the world's best mobile platform.