Zelig is correct re:Office. Windows Phone 10 will have Office, but not regular Windows.
Per-monitor DPI scaling would be nice at work. I thought that was a Windows 8 or 8.1 feature, but I may be incorrect about that as I have Windows 7 at work, and don't have much of a need for it at home.
I thought windowed universal (formerly known as Metro) applications were also part of 8.1. That is a fairly significant change; I can't say I'm enamored by getting yanked away to fullscreen Metro applications when using 8.0.
FLAC/MKV support is already easy enough to get on XP and later via various programs such as Foobar2000 and VLC (and perhaps a codec pack). I'm glad Microsoft is finally supporting them natively, but I already have convenient ways to play them so it's not an upgrade factor for me.
Newer icons I only care about if they display larger on the screen, and thus are more crisp. But so far it's not something I see as a deficiency in 7/8 (compared to, say, some versions of Longhorn where higher-res icons were clearly needed).
I don't know what benefit I would get from App-V sandboxing for desktop applications. IIRC, that's also limited to desktop applications distributed through the Windows Store, which drastically reduces the chances I'd run into it anyway. I suppose it would be similar to how Java applets have a much more limited view of the operating system than desktop Java programs? Not a great example given the security issues with applets, but the best I can think of now.
And Edge is great, particularly as a developer. I hope all Windows 10 users use it and no one uses IE on Windows 10. As a user, though, it's still one of many browser options, and I'm pretty happy with Firefox and Vivaldi going forward (and still use Opera Presto fairly often, though less recently). Edge seems to take Microsoft browsers to the point where the developer part of me wouldn't hate me for using it, but I'm not sure it goes so far as to make it the best one out there.
Did they ever get rid of web search results and MSN articles showing up in the taskbar search, a la Ubuntu One? That's my #1 annoyance with the build of Windows 10 I tried. I haven't used it that much though, since the Insider Preview's privacy policy was not very favorable and I didn't want to do any real work on it as a result. I expect the final release's privacy policy will be much more similar to previous versions, and hope the eventual trial version also has a more moderate one.
All said, per-monitor DPI is something I may well upgrade for at work, I just thought it was 8.x. Everything else, take it or leave it for my workflow.
Windows 7 and Windows 8, at current prices at places such as Micro Center and Newegg, are actually cheaper than what the planned prices for Windows 10 are, for fresh-install/pre-Windows 7 upgrades. Granted, only by $20 or so, but for a Vista or XP computer, it makes more financial sense to buy one of those and then optionally upgrade to Windows 10 for free than to directly buy Windows 10.
Edit: One other noteworthy Windows 10 improvement is native virtual desktop support. In theory I can see that as being a good reason to upgrade, but in practice I've never used them extensively even when I was using Linux, so I'm not sure I would make use of it in Windows 10, either. Still, a reason to consider.
