For my part, it started with a distaste for the Win8 UI, and the fact that they didn't pull every bit of that out from 10. I played with one of the dev previews

For my part, it started with a distaste for the Win8 UI, and the fact that they didn't pull every bit of that out from 10. I played with one of the dev previews for a bit (a couple hours, probably), and I didn't like that the local OS pushed for connections to online resources (Cortana, the default assumption that you'll link your MSN account to the machine). I really dislike features that blur the line between my computer and the internet. I don't like the forced-schedule updates, especially when Microsoft is increasingly using the update mechanism for behavioral changes in the OS. Those are things that I would've probably come to terms with sometime, or taken the time to find a work-around for. At one point, I'd made the decision that after a couple of years of Win10 being out, I'd consider an upgrade (assuming that the claims of increased performance stood up in the real world). What completely turned me against it is the determination with which they've decided to pursue getting people to use it, going as far as several levels of trickery. It's the difference between "Here, have a cookie if you'd like." and "Eat this cookie. Now." that upsets me.