Windows 10 is what Windows 8 should have been, i.e. an incremental improvement that's adapted to the new form factors that have become prevalent since Windows 7 launch. Last time I used it wasn't as polished, i.e. there were some bugs and some stuff they could improve, but those can and will be corrected with future updates. The major downside is that once you install it, you relinquish some control over your computer with potentially more to lose down that road. This means for example, that from now on, you don't have any control over the computer's updates. That's probably not an issue for most users, but who knows, occasionally microsoft might scew up on an update and there would be nothing for you to do about it. The other thing to keep vigilant about is protecting your privacy. There's a ton of ways with which Microsoft can get to your data and use them for God knows what. For the time being, they can and are used to serve you with ads on the OS you paid with your hard earned money. That's unaccaptable. So, do your research and find the privacy settings you need to turn on so you won't face that.
But other than that, it's a pretty great OS. Either way, before you upgrade, backup your Windows 7 in another hard drive and if you try windows 10 and you don't like, revert back to Windows 7. It should also be said: There's nothing wrong with Windows 7 so far and I can't think of a function that compels me to upgrade to Windows 10 right now...