Though the parent topic is a few months old, I just ran across this particular thread. Let me preface this as someone who has run Windows 8 since the developer preview, had a launch day Surface RT, and currently has a Venue Pro 8 and multiple laptops/desktops running Windows 8; I I like Windows 8 but also recognize several flaws, which though 8.1 and subsequent updates help, still exist. There were a several issues with Windows 8 that caused its bad reputation:
1. Hatred of Microsot: Let's address this up front. Yes, there was a lot of 'hatred' of Microsoft that prevented that prevented Windows 8 from getting a fair evaluation. (I put 'hatred' in quotes because I don't know that it was really hatred as such, but it was cool to slag Microsoft and everything they did, especially since it was different.)
2. It was shockingly different from what went before (basically Windows 95 through Windows 7) for basically 'everyone' who wasn't closely watching what Microsoft was doing, and yet offered no help or concession to users. Seriously, this can't be underestimated. The first version of Windows that reached broad popularity was Windows 3.0 with its Program Manager and File Manager interfaces. That was a severe change from DOS, and I remember many users decrying its WIMPy (WIndows Mouse Pointer) interface, and then when Windows 95 came out and was even more like the Mac, Microsoft had its "Start me up" campaign to promote the start button, and when Windows 95 launched for the first time, there was the huge arrow indicating to point to the start button. Even so, people back in the day used to revert to Program Manager (progman.exe) and File Manager (filemon.exe) in Windows 95 to make it more like Windows 3.x. As time went on the Win9X interface become more acceptable and became the standard. Even with Windows 7, I've seen people revert to a Windows 2000 (very close to the old Win95) type theme to feel comfortable. But with Windows 8 there was no going back, no comfortable transitions, and there was no tutorial or campaign to try to make people feel comfortable with this new interface. That changed with Windows 8.1, but by then, Windows 8.x had acquired its reputation. (You don't get a second chance to make a first impression....)
Expanding on this further, the original Windows 8 interface was very foreign to new users used to the Win9X paradigm. I originally didn't think this was really true. After all, it was just replacing the start menu with the start screen, right? Except conceptually that wasn't strictly true. In the Win9x (meaning everything from Windows 95 through Windows 7) interfaces, when you booted up the computer, it came up in the desktop. It didn't boot up with the start menu open. But in Windows 8, it booted to the start screen. And when you closed an app, in the Win 9X interfaces, it went back to the Desktop. In Windows 8.0 it went back to the start screen. This changed the 'anchor point' of the system from the desktop to the start screen. (The Windows 8.1 updates have changed this behavior quite a bit.) In some respects, it was a reversion to a Windows 3.x type interface where file management was completely separate from app management; this undid almost 20 years (literally a generation!) of user interface expectations.
3. After all these changes, the apps using the new interface/API were awful. I could write pages on this, but to try to cut this down; do you remember the original Mail app? Seriously, email is a primary use case for most people, and their broadband cable accounts are one of their primary accounts. Most of those are POP accounts. What type of email account did Windows 8.0 (and for that matter, the latest 8.1 version) not support? POP mail. So if a regular user managed to figure out the UX changes sufficiently to get to setting up email they'd get the 'poke in the eye' for not being able to set up their email. The absolute worst case was when the email app was updated to have a POP mail account option. Selecting that got an ever so helpful message that POP accounts were not supported. That happened to a coworker of mine with a new computer; literally, he was so angry at that point that Microsoft might just as well finished the dialog with a statement like "go f*** yourself, loser")
4. The bizarre insistence that Windows 8 (Metro, Modern, Windows Store, whatever) apps couldn't run windowed, but had to run "full-screen" or half screen, or whatever bizarre vertical slice of the screen Microsoft insisted on. This actually drives me nuts on a multimontor computer, even today with the latest Windows 8.1 updates. Here's a case that happens all the time. I've got a Windows store app full screen on one screen (maybe email, Xbox Music, etc, who cares), and on the other screen I've got the Windows desktop. So I need to look at one window on the desktop, so I move another off the screen, even just partially, to the other monitor. But Metro apps are such special pure snowflakes that they can't share the screen with lowly desktop apps, so they disappear. Then I move the other desktop app back and look to the other screen. Oh, the Metro app has gone off and had a sulk so I have to go find it and console it.... Now I understand and fully appreciate what's going on, but it momentarily interrupts my workflow. But this absolutely necessarily because there's no way whatsoever that Windows 8/Metro/whatever apps can overlap/underlap with Desktop apps. Except the Windows 10 tech preview comes along and all of a sudden there's no problem mixing Metro and desktop apps.
But other than all of the above, Windows 8 was perfect, and it's only ignorance that affected the adoption of the OS. Seriously, there were good aspects, but also horrible aspects to Windows 8 that Microsoft is just recovering from.