Well, for me personally, here's the reason I don't like Windows 8:
1. It's not how I'd change the UI to make things more efficient.
Now, understand that in Win7 I've "removed" the start button and have my own organizational method for UI via various programs. I understand that it'd not necessarily be efficient for anyone else to use, and it really is just a "fits just me" thing. However, that doesn't mean that when the new UI for Windows 8 is basically a 180 of how I'd do things, it won't affect me. It just means I'm only able to represent myself. Hence why I say "I don't like Win8 UI", rather than "Windows 8 UI is bad".
2. It was too drastic a change, too fast.
Personally, they could have salvaged the feelings people had right off the bat had they kept both options in this version of Windows.
- Have the desktop screen still with a start button (with the option to remove it in properties).
- Add a Metro UI button next to the normal start button so you can proactively sample it from the desktop screen.
- Have the "first time starting Windows" ask if you want normal desktop to be the normal startup, or the metro UI. Give the option to change this in startup options, easy to find (maybe have it in the Metro UI screen as a checkmark option).
Save a full Metro Only for the next PC version, or for tablet/phone only version now.
As it stands, it felt like a parent saying "Time to learn to swim" and tossing the kid into the deep end. A lot of casual PC users I encountered (family and customers in my profession) certainly acted like they were drowning. Frantic and shutting down. It breeds resentment, and no matter how much more efficient something might be, slapping a learning curve in the face is going to make a casual user forget to know how to learn (I experience this DAILY in my profession for other things, OS UI learning is no different). Even asking someone to do something they normally do causes people to freak out when they think it's new (I've had conversations devolve into "How do you normally turn it on?" and the response is "I don't know!", /sigh).
3. Flexing market control to inflate purchases.
I can't really fault them for doing this, as a business it makes the most sense. Pull anything not the new product (OEM). Disallow future updates on universally used stuff to anything but the new product (DirectX). I can understand why they did it.
Then again, I can understand why they sell their product for money. I still prefer open source methods for things rather than gunning for profit margins. I won't condemn them for it, but I don't have to admire them for it. There's an acceptable level of profiteering in my personal opinion. Some of the things these companies do, while legitimate, feel less than "customer oriented".
Also, "backward compatible when possible" is a big factor in how I look at things.
If I had the time and focus to build my own OS from slackware, I would do it. *shrug*
All of this gives me a negative opinion of the OS. Will I still use it the next time I get a PC or laptop upgrade? I don't doubt it. But you can bet I'm going to tailor it up as much as I did my previous OS.
And I'm certainly not going to approve or applaud the way they handled this.