I've elected to try Windows 10 on my laptop while holding out on my desktop.
The UI is an improvement over Windows 8.1 in some regards, though functionally it's not much different from Windows 7. It's fairly responsive, but the difference between Windows 7/8/10 seems minimal. I have not noticed any improvement in boot times over 8.1, and both it and 10 tend to use more RAM than Windows 7. Unless you enjoy Windows metro apps, Windows 10 comes with an assortment of pre-installed applications that are harder than ever to get rid of.
Task View is nice. The flat design is refreshing if you're into it.
But as mentioned above, this is Microsoft's most intrusive OS yet, and you have little to now expectations of privacy here. If you know what you're doing it's not too difficult to debloat Windows 10 stripping it of Metro apps and forced integration of OneDrive while also blocking most host connections to Microsoft servers. But it's quite annoying to do. And unless you have the Enterprise version of Windows 10 you have no option to completely disconnect yourself from Microsoft telemetry.
DirectX 12 promises greater performance in games, but for now Windows 10 doesn't seem to play nice with older games.
Edge isn't perfect, but it's a much improved browser compared to Internet Explorer.
Is it worth upgrading from Windows 7 Ultimate? That depends. If you like a modern interface but more desktop friendly design choices than Windows 8, and if you don't mind privacy issues too much, and you mostly rely on your OS to be comfortable and easy to use, then Windows 10 maybe worth it. I may eventually go back to Windows 7 Ultimate however, at least on my laptop. Windows 10 at the moment isn't as customizable or low profile as a properly configured Windows 7 installation can be.