Phoronix features today a review of Windows 10 that's a little different from most you might read, because it's specifically from the point of view of an admin who uses both Windows and Linux
daily, rather than concentrating only on the UI of Windows qua Windows. Reviewer Eric Griffith finds some annoyances (giant start menu even when edited to contain fewer items, complicated process if you want a truly clean install), but also some good things, like improved responsiveness ("feels much more responsive than even my Gnome and KDE installations under Fedora") and an appropriately straightforward implementation of virtual workspaces.
If you're on Windows Vista, or Windows 8/8.1, then sure, upgrade. The system is refreshing to use, it's perfectly fine and definitely an upgrade. If you're on Windows 7 though? I'm not so sure. ...
Overall, there's really nothing to see here. It's not terrible, it's not even 'bad, it's just... okay. A quiet little upgrade.