It's a replacement, but that's a subjective statement. For some people, like myself, I wouldn't bother with Win10 just yet. I'd wait until all the bugs are out, and they clean up the way it handles a lot of protocols. For the majority of users, it can be hit and miss.
Realistically, Win10 is a highly subjective "upgrade" for most people. I'd say try it on a spare computer, or in a virtual machine, and give it a try that way.