|WP8.1's transparent Live Tiles,|
Cortana and new notification bar
The big recognition point will be Cortana, Microsoft's answer to both Google Now and Siri. Given that this is beta and very much pre-release the functionality and quality of recognition is fantastic. Having the Cortana live tile surfacing information that you tag as important in your notebook works as well as Google Now, even if the range of things reported on is quite limited at the moment. (To be fair that may be because I'm using a US service in New Zealand).
The second high profile change is the arrival of the action centre. This single place for accessing notifications doesn't stray far from the mould created by Google and copied by Apple: swipe down from the top of the screen to gain access to four (customisable) shortcuts, and details of all the alerts from applications that you have tagged as worthy. The top bar previously only accessible through a downward swipe now becomes omnipresent, meaning that time, power and network status are always available.
Microsoft have updated it's keyboard with Word Flow - a swipe style word tracing service that outperforms any I've previously used. It's quick intuitive and manages to do a better job with punctuated words than similar products on Android. Certain words will also surface appropriate smiley style icons - phone and car being two examples. It's a nice touch which typifies the consideration that Microsoft has given to this release.
Changes to the live tiles won't be to everyone's taste, however none are enforced so if they don't float your boat you can just disable them. Owners of large screens (4.5" according to Microsoft) get to choose between the two and three column layouts. It's also possible to turn your live tiles transparent and display an image behind them. Having tried this on the Lumia 1020 I can say that the latter works very well, however I'd be inclined to stick with the two column layout on the 4.5" screen, otherwise it can get a bit messy in there.
There are new intelligent controls for WiFi and battery. The former had some clever tricks up it's sleeve - it will find friendly free WiFi hotspots and register/connect to them automatically. It also allows you to share your home WiFi with friends without having to give them your passcode. Of course they'll need to be using Windows Phones too if they want to take advantage of this function.
Microsoft has updated the calendar, adding a new week view and swipe scrolling between views. It looks as good as ever and works well.
There's also support for Miracast displays for those handsets sporting the hardware to use it - only 2014 Nokia handsets at the moment.
All in all I found the upgrade to be a significant improvement in the Windows Phone feature set. To the point where the only reason for not buying one would be the absence of an application that you must have from the Market. By the time the update gets released into consumers hands Nokia will have added its own update to the mix, which should make the new 2014 Lumias an even more appealing prospect.
Appealing enough to tempt iPhone and Android owners? I think it's entirely possible - Windows Phone looks better, it's now feature competitive and available on a wide range of hardware. For an increasing number of people that means that Windows Phone is now a viable option.