1. Holy privacy violations, Batman! While Google has only become evil in the past decade, Microsoft has never stopped being evil. There are a whole lot of data transfers from Microsoft to you and from you to Microsoft set as default in Windows 10. Among these are mandatory Microsoft updates (both security and non-) and (voluntary) contributions of all sorts of data from you to Microsoft. Cortana (Bing voice search, basically) I have neither used or enabled, as I consider it too invasive to turn on.
2. Metro Internet Explorer is gone. What’s the point of Tablet Mode with no Metro Internet Explorer? And Edge is hardly a great tablet browser like Metro Internet Explorer was.
3. With Microsoft Edge, Microsoft has narrowed the gap with Firefox&Chrome almost by half. Unlike Internet Explorer, at least it loads all the content in a webpage with some reliability. It also has the most attractive desktop user interface of all the major browsers. Edge also has a very good built-in PDF rendering function, thus making it the default PDF viewer in Windows 10. However, there is no “Open File” button in Microsoft Edge that I can find, so I don’t see why Microsoft made it the default PDF viewer while omitting this feature. This PDF rendering capability, however, was also brought to Microsoft’s Reader App in an update around July 28, so there’s no need to upgrade from Windows 8.1 to 10 just for this feature. Edge is a memory hog like no other. At present, when I have only eight tabs of Google.com open, Edge is using nearly 400 megabytes of memory. Also, for some reason, Edge does not deal well with horizontal scrollbars in webpages. It also continues Microsoft’s four-year-long tradition of interpreting blatant search terms as addresses. I would suggest sticking with Firefox or Chrome for now. Microsoft has been routinely bad at improving and innovating web browsers since 2003 (the nadir: Internet Explorer 8).
4. The added user-friendly displays of disk space and Internet activity in the Settings App look nice.
5. The Tablet Mode has some good parts, but is not yet a clear improvement on 8.1. The Task View is definitely an improvement on 8.1. The Start Screen is slightly improved (it has more empty space, but there’s more freedom in moving the tiles). The permanent taskbar is obviously a replacement for the Charms (it should have been an impermanent taskbar, which would have been called up in the manner of the Charms), and Desktop programs opened in Tablet mode have occasional difficulties in automatically opening new windows. This makes it difficult to recommend it for either tablet or desktop users. There’s also the curious omission that desktop apps cannot be split-screened, but they couldn’t have been split-screened in Windows 8.1, either. Also, as all desktop apps are fullscreen in Tablet mode, even if they were never designed to be, the Tablet Mode may be somewhat worse than the barely-sensible desktop-as-an-app system in Windows 8.1 at displaying desktop apps.
6. The Start Menu is clearly a redeeming feature in Windows 10. It replaces the desktop in Windows 10 tablet mode, and works similar to the Windows 7 Start Menu in Desktop mode. There are live tiles in the Start Menu. The location of the live tiles is much more customizable than it was under Windows 8.1. The list of programs is vertically scrollable in All Apps view and is accessible from Start.
7. The twice-renamed Zune Music and Video apps and the XBox App need to be uninstalled (and not re-installed again) by PowerShell commands if they are ever to be uninstalled (and not re-installed again).
8. There is a multiple desktop feature in Windows 10. This allows the intuitive opening of multiple processes of the same program, one in each desktop. This is unique to Windows 10.
9. The ability to create a Guest account has been totally removed. Of course, this is avertable by making the signin an image that’s extremely obvious to figure out to guests.
10. The Windows DVD player is only available free for one year, and is very limited. Seriously, I have no idea why it exists (or why Microsoft is charging for ad-free Solitaire and Minesweeper).
11. The ability to display Metro apps in the desktop is nice, but there’s no way to make some of them fullscreen! The Photos app, for example, does not display genuinely fullscreen in Windows 10 the way it does in Windows 8.1, and, indeed, looks kinda ugly. The split-screen mode in Windows 10 is neither better nor worse than in 8.1.
12. The default OneNote app has suffered a massive feature downgrade, as is readily visible from the comments in the Windows App Store, especially for tablets.
13. Windows 10, unlike Windows 8.1, allows you to sideload Windows Store apps without a license.
15. Update: Windows 10 also has a resizeable Start Menu and a better Snap view (corner-snapping!), which I haven’t noticed before. This makes an upgrade more tempting. Edge has also improved. Fast Startup (from hibernation file) came to 8.1 during the week of the release of Windows 10.
In short, there are too many downgrades for me to decisively recommend Windows 10 over 8.1. I certainly don’t recommend Windows 10 over 8.1 on any touch-centric device (including Windows Phone), and will probably not ever do this, as Microsoft seems to have de-emphasized touch permanently. So I’m temporarily switching back to 8.1 on my main computer (this is only allowed for one month after Windows 10 installation) until Microsoft either ends its customizability removals, improves Edge to the point it’s recommendable over Firefox or Chrome, or offers some other decisive new feature making Windows 10 superior to 8.1. I recommend the Windows 10 upgrade only for Windows 7 users, as it allows them to install Windows Store apps. For Windows 8.1 users, it offers no decisive advantage. Windows 10 is a work in progress, and may be decisively superior to Windows 8.1 sometime in the future. But Windows 8.1 is an established operating system, with less uncertainty about its features or lack of them. I’ll probably go back to Windows 10 by July 2016, if only to experience new features missed out on by Windows 8.1 users in the distant future. But if Microsoft continues limiting Windows 10, I’ll doubt I’ll ever go back to it.
Update: I have gone back to Windows 8.1. All programs I’ve installed after switching to Windows 10 are gone. All my Firefox history remains. I forgot to mention that Windows 10’s startup time (from power button to lock screen) is much faster than that of Windows 8.1, not to speak of Windows 7.
Update 2: If some Windows Store apps aren’t installing after the reset (esp., Fresh Paint, OneNote, Tubecast), you may need to install the Flixter app for reasons specified here.