To answer that, you have to differentiate between 8 and 8.1. The biggest problem was the new Start menu, the only way I could live with 8 was to completely replace it. 8.1 was okay, but by then many were already convinced they wanted nothing to do with Windows 8. Much like what happened with Vista. By they time they released SP2 for Vista, it was not too bad. But people were already convinced they wanted nothing to do with it.
IMO, Windows 10 is complete crap and I will never pay for it. In fact, I think it is so bad that it isn't worth anything. They earn enough money already from ads and selling the collected data to ad companies. KDE Linux looks much better, is free (in both senses of the word), free of ads and spookware.
Okay, I'll byte. If Windows 10 is "complete crap" and not "worth anything", why are you here participating in a forum dedicated to discussing Windows 10? Not that I object, mind you, it's a free country, but it just makes me wonder ...
I don't recall ads in Windows itself. There are so many ads on web pages these days, and more and more sites are giving me a hard time about using an ad blocker. Years ago I used the really large HOSTS file, but these days that blocks sites that I actually need to access. I don't think we're going to win this battle, I think we're going to have to accept a world full of ads. For right now, I am using the new Edge (without an ad blocker) to access sites that won't work from Chrome (where I do use an ad blocker).
There aren't that many third party ads in Windows 10, but in Windows 10 Home (and Pro also AFAIK) if you don't sign in using a microsoft account, don't use Edge as the default browser, and don't use onedrive, you will be nagged every three days at logon to do so.
I consider it similar to open candy and thus consider them adverts. If a company pays another company to bundle a completely unrelated app, I consider it an advert. For example, many 'free' proprietary apps make money by being paid to bundle unrelated (and sometimes malicious) apps. Although Candy Crush isn't malware, why does Microsoft need to bloat a $200 OS with sponsored apps? Also, if you don't consider them adverts, Microsoft will show you ads for Microsoft store apps in the start menu app list and pinned tiles. Although Pro Education, Education and Enterprise don't have ads, you can't just buy them individually.
Those $5 keys are illegal, and is as illegal as using an activator, and of course using an activator is free.