I discussed this matter with my younger brother, a computer professional:
I bought my computer, a Dell Inspiron 570 Desktop, with Windows 7 installed. However, Windows 7 seems to be on the way out. He recommends that I upgrade to Windows 10, and first view a video available on YouTube to see what it’s like. (I know that Internet connection is not possible with Windows 10, but I abandoned that years ago.)
So I would like to know what I should know before I go to the trouble of installing Windows 10.
One known issue is that the default Windows 10 installer includes a lot of crapware, and you have to run a script to remove it.
For instance GitHub - W4RH4WK/Debloat-Windows-10: A Collection of Scripts Which Disable / Remove Windows 10 Features and Apps or Reddit - Dive into anything
It also very heavily endorses the use of Cortana and Edge, which gather information about pretty much everything you do and report it back to Microsoft, ostensibly so they can better tailor your computer’s operations to your needs. If you don’t want that happening, there are some specific settings to change during a custom install which kind of trims them back to a reasonable level. I’m not sure how well that works (there have been a few updates since I upgraded, and Cortana’s running again). I only ever used Edge once, to download Chrome.
Thanks to both. 
ZDNet is an excellence resource.
More information than you’ll ever want to know (and some of which won’t apply to you).
My computer has a clean installation of Windows 10 and I never use Cortana and, when I do need to use Internet Explorer, use IE11 rather than Edge. IE11 is still on the system, but you have to go to a bit of effort to run it rather than Edge. I don’t see much “bloat” in the Windows 10 installation.
And the OP says that “Windows 7 seems to be on the way out”. There’s no “seems” about it; the mainstream support period for Windows 7 ended in January 2015, while the mainstream support period for Windows 8 ends in January 2018. So both are effectively obsolete.
It works 98% the same as previous versions of Windows. Some stuff looks different, some stuff has been moved around, and new features have been added.
It’s a minor point, but you simply can’t run the game Civilisation 4 on Windows 10. 
If you prefer the interface on Win 7 check out Classic Shell.
The major thing you need to know is that for the most part Win10 updates when it damn well wants to. You can set a period as work time, but that is short enough to be pretty useless. However it often saves your state pretty well - not always, but sometimes.
I got rid of the damn tiles, and the learning curve from Win 7 or even Vista is very small. Don’t use Cortana and use Edge only when I absolutely have to. So far (over a year) so good.
Without getting into my usual harangue about Microsoft’s policies of generally unproductive forced migration to new operating systems – something that many large enterprises scrupulously avoid through custom support contracts – I will just point out that Windows 7 SP1 will continue to get security updates until January 14, 2020. As far as I’m concerned, a system supported by a quality anti-virus product, with valid root certificates for SSL connections, is a perfectly viable system, and bonus if it still gets security updates. YMMV.
They support their OSes for far, far longer than Apple does.
I switched as soon as I was able on both my desk and laptop. Any problems have been minor irritations like strangling Cortana and avoiding Edge. I use Chrome without problems and use Ad-block. I really don’t see why this resistance.
Updated do arrive, though less frequently than they used to, and I leave them to get on with it when I close down at bed time. Of course, having a fibre internet connection helps - I guess that someone with a meter and low bandwidth might be less happy.
You can play it using Steam (Complete edition is £14.99 at the moment) just not using your existing disks 
Slight hijack about Cortana - does it replace the Search bar from earlier versions?
mmm
Using the standard Windows 10 shell, yes. The search bar embedded in the taskbar is Cortana.
Using Classic Shell, there’s a separate search bar (a la Windows 7). Dunno if it’s Cortana or not; it doesn’t advertise itself as such, but I wonder what search APIs are available to Classic Shell to carry out searches, other than Cortana. If the filesystem search capability from Win 7 carried forward and Classic Shell uses that, it’s possible that it’s not Cortana.
Some of these answers are a bit crotchety. Sorry if that sounds insulting.
I will say that I agree that Edge is kind of a buggy mess, it might end up being a good browser but the currently-shipping version is a long way from that. And I don’t like that it’ll occasionally install a Windows Store app for you-- no I don’t want a copy of Candy Crush.
There’s a lot of stuff it handles much better, though. For example if you have two monitors that need different scaling-- it’s not 100% perfect in Windows 10, but it’s a heck of a lot closer than any previous version of Windows. If you play games, the porting of all the Xbox One features to Windows 10 is pretty amazing-- I love “Xbox, record this” (or whatever it’s called). Amazing feature. It also has the usual performance improvements. Startup, in particular, is a lot faster because it basically always hibernates the core OS components so when you reboot it just has to load that hibernation image into RAM then load your apps, instead of initializing the OS. Memory compression helps the OS keep more stuff cached in memory and use the disk a lot less.
The privacy concerns are overblown, IMO. Microsoft sends voice samples to their servers when you use voice recognition to run algorithms on them to improve their voice recognition. It’s exactly what Apple is doing with Siri, and Google is doing with Google Assistant, but for some reason there’s a near-panic over Microsoft doing the same thing. If you use Siri, you’re already sending just as much data to Apple as Microsoft’s sending to their servers.
It’s different than Windows 7, but it’s not insanely-different. You’ll get used to it in only a couple hours if you give it a chance.
I got a new laptop last Fall which came with Win 10 installed. Before I started it up, I read four or five tech websites that described what changes I might want to make re privacy, start up items, defaults, start menu, etc. I took notes and it took me a several hours to work through the list. I downloaded Firefox and disabled Cortana.
A couple months ago I finally got around to wiping my old Win 7 laptop and downloaded a (free) version of Win 10 from the Microsoft website, I forget what it was called, the Developer’s version, something like that, but it is still available. I don’t have my notes anymore but I did basically the same stuff. I’m only using this to steam movies.
There are online reports of people who still had their CD key being able to contact 2K via their web site support form and were emailed the Steam key for free.
RE: Classic Shell–Agree with everyone else–if you want, you can use it and some online guides to turn the look and feel back to Windows 7 if you wish–including the quick launch bar, start button, etc.
That’s what I did, but they stopped doing that earlier this year.