Microsoft finally rolled out the very first build to its Windows Phone 10 OS and while it brings a new look and a few good changes, this will be the very first reason why you shouldn't install the build...
1. It's the first build, from an engineering standpoint, an alpha build, the very first build will always consists of numerous bugs and it's the most unstable of all the builds before the final release. Imagine you had an idea, well the first build will be the very first implementation of that idea and it's at this stage you find a lot of bugs and how unstable your idea is.
I have had the build on my Lumia 635 for 24hours and I have to tell you, I have had to force reboot the device a few times since.
Recommendation is to leave this build to more technical minds or if you have a second phone you can test it on, if not, then skip this.
After the kinks have been resolved, the next build should be worth it.
2. Missing universal apps: While the demo video from Joe Belfiore shows off the universal apps like Microsoft Word, Excel and Powerpoint. They are missing from this build. The only universal apps I could find were Calculator, Photo and the Alarm apps.
3. Half baked apps: While some universal apps are missing, the universal apps that are present in this build are somewhat incomplete, like the photo app, the messaging app or the phone app. It is clear some features from these apps are missing. For instance, during the Windows10 event, Joe Belfiore talked about how Skype will be integrated into the messaging app (just like Google's hangout app), well that doesn't come in this build.
4. No Outlook mail app: Another universal app that doesn't make its way to this build is the Outlook mail app, it is already getting rave reviews in the Android and iOS stores, no joke you can search "outlook mail" on twitter and hear what iOS and Android users are saying about it, so you can imagine how bummed I was when I found out it wasn't available yet in this build.
5. Outlook Calendar: This also didn't make it to the first build of Windows Phone 10. Hopefully it will as WP10 becomes available on more devices.
6. Buggy Cortana: If you enjoy the world's best digital assistant, then you might want to skip installing the first build of WP10, as I have come to find out, she is very buggy and doesn't work half the time, frequently responding with "something is wrong..."
7. No dark theme: The new WP10 OS brings with it a few UI changes, and the white theme is now predominantly used, like in cortana's page and in settings. There is already a lot of feedback to bring back the dark theme, so it might come back in the next build? But in the meantime, if you fancy the dark theme, you might want to skip this one.
8. Slow performance: It's slow, using the Windows 10 build is awfully slow. enough said.
9. Constant freezing: Also with this build comes constant freezing, like I pointed in my first point, this is the first build and with it comes a lot of instabilities and bugs.
10. It's just not worth the hype: After release of the first Windows 10 PC build and the brief demo of the Windows 10 Phone at the Windows 10 event last month, the anticipation has been high for its release but after using it for a day, it is not worth the hype, I know it is an alpha build and as such it is buggy but we were expecting more, a lot more, I'm talking the new universal apps, the new outlook apps, the Skype/SMS integration, resizable keyboards all missing from this build.
And the fact that the build hasn't been made available to high end Lumia devices just sums it up.
Most of the new features in this build could easily have come as a GDR2 or 3 update.
Microsoft is on the right path here and the purpose of this build is not to impress its users but to ask your help in reporting bugs and giving your suggestions. So if you are up for it, if you have a second phone, we urge you to join the team and give your feedback to make Windows 10 the best mobile OS out there. But if you are looking for an update/upgrade to your Windows Phone 8.1, this is NOT for you.