I thought I would share my experience of Windows 10 running on a slightly older, but capable Lumia 925 (since most reviews come from experiences on much newer devices).
To save you reading the whole post.... Should I install this build on my Lumia 925? Bottom line: No. Unless you have a constant access to a power socket and carry around your charger with you, you're not going to get more than an hour or so of useful time. During that hour you'll be tearing your hair out while trying to browse the web.
FYI - I tried installing Win10 on an old Lumia 520 - my advice, don't even bother. It's unusable.
Here's my experience of the things I've looked at in the last couple of days. It's by no means a comprehensive review.
Performance
Any long time user of the 925 will tell you that things started to go downhill in the performance stakes with Windows Phone 8.1. The buttery smooth, lag-free experience of the device with 8.0 was compromised. That's not to say that the device was not still perfectly usable and the lag here and there wasn't overly annoying - I just couldn't tell people it was super-smooth any more.
With Windows 10, the general experience is much the same. Edge has moments where it (yes, I'm going there) "seems faster", but on the whole it suffers with lockups and periods of unresponsiveness (to be expected at this early stage).
The big downside is this. What performance that Windows 10 does eek out of the device seems to be maxing out the CPU nearly all of the time. The device is almost too hot to handle and that is reflected in the battery performance. During a one hour train journey using cellular data my battery was completely expended. The battery usage app in Settings tell me that in the last 24 hours 44.3% of my battery life (by apps) was spent on Microsoft Edge and 63% of overall consumption was powering the display. (I mostly use the browser, the default Twitter app, the new Outlook email and calendar apps).
The phone has bouts of general unresponsiveness. Swiping down to get to the Action Center can be infuriating. One swipe down in 5 might work and sometimes not at all - the same is true for dismissing the action center. Some of the action center quick actions seemingly become unresponsive after some time and you'll notice the icon flashing (I'm unsure what the significance of the flashing is).
Apps
Now, this will differ for everyone depending on the apps you use, but in terms of app compatibility, most of my apps continue to function with the exception of Wunderlist and OneNote. Wunderlist will not open and it immediately crashes. I still have pinned Wunderlist lists which have persisted, but are obviously of no use. The same is true for OneNote. I have pinned notes on the Start screen, but the app is simply not present on the device, nor in either store.
The new Outlook apps are excellent. Finally a great calendar app (although Chronos Calendar + is a great third party app) and the email app brings all your accounts under one app. It's intuitive, fluid, fast, supports both portrait and landscape modes and looks great. These two alone are well worth playing with.
The updated weather app also looks superb and very modern.
Camera
The camera is much the same, although I'm not entirely convinced the focus is correct. Either that or the quality is reduced. I haven't spent that much time with the camera admittedly, but there does not appear to be enough to consider upgrading your whole OS for. It definitely loads a lot slower from a long press of the hardware button. I'm not sure what firmware is installed since the extras and info page has no information on this (where it used to say something like 'Lumia Denim'. After installation I saw the notification 'Welcome to Lumia Cyan' so it's possible that the performance improvements on launching the camera in Denim have been lost (at least I think that came in Denim).
Microsoft Edge
As I said, the browser has occasional moments when it seems a lot nippier than IE. But the obvious power drain, lockups and unresponsiveness detract from that benefit. The browser seems to struggle rendering sites such as Windows Central. It might render part of the page only, meaning you can't scroll beyond a certain point, or it might allow you to scroll down but present you with a blank (white) screen for several seconds. When clicking on links you might not see any indication that the link has been clicked (no link colour change or underlining) and the browser has no progress indicator which would let you know the link has been clicked. Overall the experience is generally slow and laggy. Sometimes it just locks up completely. A restart of the app does seem to temporarily alleviate some of the issues, but not for long.
Most of the usual browser features are there, but getting to your favourites is more clicks than is necessary which becomes more annoying with time.
It would have been nice to leave IE installed alongside Edge as a fall back.
Other Deal-breaker Issues
The mobile hotspot is not working at all for me and it's something I use all the time. It simply tells me there is no cellular data, even if I have a full strength 4G signal.
The Action Center buttons gradually become disabled (see flashing icon issue mentioned earlier).
Pinned contacts do not launch the People app without crashing it.
New Features
I see a lot of promise and refinement and will be excited to install the next build. Little things like quick access to the flashlight in the action center are a nice, and useful, touch. Being able to reply to text messages from a notification is a time-saver. The apps list is better organised, with recently added apps at the top. In all honesty, there aren't tons of new features for me to get excited about. The new apps will be bringing the most to the party in my opinion.
What I care about is a lag-free, responsive experience, with equivalent or better battery life and a world-class browser. Unfortunately, it's not there yet and therefore I could not recommend this build for daily usage on the Lumia 925.
To save you reading the whole post.... Should I install this build on my Lumia 925? Bottom line: No. Unless you have a constant access to a power socket and carry around your charger with you, you're not going to get more than an hour or so of useful time. During that hour you'll be tearing your hair out while trying to browse the web.
FYI - I tried installing Win10 on an old Lumia 520 - my advice, don't even bother. It's unusable.
Here's my experience of the things I've looked at in the last couple of days. It's by no means a comprehensive review.
Performance
Any long time user of the 925 will tell you that things started to go downhill in the performance stakes with Windows Phone 8.1. The buttery smooth, lag-free experience of the device with 8.0 was compromised. That's not to say that the device was not still perfectly usable and the lag here and there wasn't overly annoying - I just couldn't tell people it was super-smooth any more.
With Windows 10, the general experience is much the same. Edge has moments where it (yes, I'm going there) "seems faster", but on the whole it suffers with lockups and periods of unresponsiveness (to be expected at this early stage).
The big downside is this. What performance that Windows 10 does eek out of the device seems to be maxing out the CPU nearly all of the time. The device is almost too hot to handle and that is reflected in the battery performance. During a one hour train journey using cellular data my battery was completely expended. The battery usage app in Settings tell me that in the last 24 hours 44.3% of my battery life (by apps) was spent on Microsoft Edge and 63% of overall consumption was powering the display. (I mostly use the browser, the default Twitter app, the new Outlook email and calendar apps).
The phone has bouts of general unresponsiveness. Swiping down to get to the Action Center can be infuriating. One swipe down in 5 might work and sometimes not at all - the same is true for dismissing the action center. Some of the action center quick actions seemingly become unresponsive after some time and you'll notice the icon flashing (I'm unsure what the significance of the flashing is).
Apps
Now, this will differ for everyone depending on the apps you use, but in terms of app compatibility, most of my apps continue to function with the exception of Wunderlist and OneNote. Wunderlist will not open and it immediately crashes. I still have pinned Wunderlist lists which have persisted, but are obviously of no use. The same is true for OneNote. I have pinned notes on the Start screen, but the app is simply not present on the device, nor in either store.
The new Outlook apps are excellent. Finally a great calendar app (although Chronos Calendar + is a great third party app) and the email app brings all your accounts under one app. It's intuitive, fluid, fast, supports both portrait and landscape modes and looks great. These two alone are well worth playing with.
The updated weather app also looks superb and very modern.
Camera
The camera is much the same, although I'm not entirely convinced the focus is correct. Either that or the quality is reduced. I haven't spent that much time with the camera admittedly, but there does not appear to be enough to consider upgrading your whole OS for. It definitely loads a lot slower from a long press of the hardware button. I'm not sure what firmware is installed since the extras and info page has no information on this (where it used to say something like 'Lumia Denim'. After installation I saw the notification 'Welcome to Lumia Cyan' so it's possible that the performance improvements on launching the camera in Denim have been lost (at least I think that came in Denim).
Microsoft Edge
As I said, the browser has occasional moments when it seems a lot nippier than IE. But the obvious power drain, lockups and unresponsiveness detract from that benefit. The browser seems to struggle rendering sites such as Windows Central. It might render part of the page only, meaning you can't scroll beyond a certain point, or it might allow you to scroll down but present you with a blank (white) screen for several seconds. When clicking on links you might not see any indication that the link has been clicked (no link colour change or underlining) and the browser has no progress indicator which would let you know the link has been clicked. Overall the experience is generally slow and laggy. Sometimes it just locks up completely. A restart of the app does seem to temporarily alleviate some of the issues, but not for long.
Most of the usual browser features are there, but getting to your favourites is more clicks than is necessary which becomes more annoying with time.
It would have been nice to leave IE installed alongside Edge as a fall back.
Other Deal-breaker Issues
The mobile hotspot is not working at all for me and it's something I use all the time. It simply tells me there is no cellular data, even if I have a full strength 4G signal.
The Action Center buttons gradually become disabled (see flashing icon issue mentioned earlier).
Pinned contacts do not launch the People app without crashing it.
New Features
I see a lot of promise and refinement and will be excited to install the next build. Little things like quick access to the flashlight in the action center are a nice, and useful, touch. Being able to reply to text messages from a notification is a time-saver. The apps list is better organised, with recently added apps at the top. In all honesty, there aren't tons of new features for me to get excited about. The new apps will be bringing the most to the party in my opinion.
What I care about is a lag-free, responsive experience, with equivalent or better battery life and a world-class browser. Unfortunately, it's not there yet and therefore I could not recommend this build for daily usage on the Lumia 925.
Facebook
Twitter
Instagram