It's not just that they changed things, which they do with every release, but that they changed things for the worse.
Windows XP to Windows 7 had some pretty major changes -- including the task bar revamp -- but I got used to it. I didn't grumble, I didn't complain, because it wasn't worse, it was just different, and in some ways better. I like the previews. I like the jump lists. Let me reiterate that: it's different, but it's not worse.
The Windows 8 GUI isn't better in any way that I can see. On the contrary, every change is a change for the worse. Things take longer. More movement is required. More clicks are required. The design is schizophrenic and unpredictable. It splits the OS into two distinct styles, neither of which is remotely complete.
That's not even considering the ridiculous decision to eliminate the start menu:
-- It breaks 17 years of muscle memory for most users. I thought I used a lot of keyboard shortcuts, but I only realized just how often I actually click the start menu when I tried Windows 8. Worse still is Windows Server 2012, where the "server manager" shortcut is in the same location the start menu used to be! If you're an admin who's used to administering Windows Server, you will be punished with a one minute wait, often.
-- The new shortcut is a tiny 2x2 pixel area or somesuch. Sure, it's easy to hit it if it's in the corner of the screen, right, because you can just 'snap' your mouse into the corner easily. Unless you have a second monitor to the left of the main one. Or you're connecting over ANY kind of remote desktop that's not full screen. Like a Hyper-V console. Or a KVM. Or VNC. Or VMware.
-- Just press the "Windows key", right? You were about to tell me that, weren't you? Well guess what, it's not always available. Some keyboards don't have it. Some remote access scenarios don't pass it through. Sometimes I'm connected through 3 layers of remoting, and it's just not going to happen. Now what? Have you TRIED hitting a 2x2 pixel area over three hops with a total of 800ms of latency?
-- Accessibility is right out the window. Some people have movement impairments, and just can't hold sufficiently still to hit such a small target. Or end up hitting it accidentally when they actually were trying to click a taskbar icon.
-- Don't even get me started about people with flickering image triggered epileptic seizures. I can't wait until the first lawsuits of users literally collapsing in a twitching heap because of the non-stop full-screen transitions between the traditionally bright desktop applications and the new tiles screen with its dark background. Thankfully I don't have this problem myself, but I've found that in a dark room when using Windows 8 on a large monitor (e.g.: 24" or bigger) my eyes water. The repeated brightness transitions are almost painful.
-- It hides content. If you want to, say, search for something complex on your machine while referencing something in an application's screen... err... no such luck, you can only search full screen now.
-- It's enforced, unlike every other GUI transition Microsoft has ever made. I'm sure it's for our convenience, and not to force a new GUI paradigm down our throats just so Microsoft can leverage their monopoly to barge their way into yet another market.
However, you have a point: the GUI changes are a mere annoyance. I can grit my teeth and get used to it. However, as a developer, I can't help but gape open-mouthed at Microsoft stunningly myopic "strategy". Put yourself in the shoes of a Microsoft Windows developer wanting to write a new full-featured, heavyweight Windows desktop application. Here are the options:
-- Win32: the assembler of GUI programming. Often referenced on microsoft.com as the "legacy" API.
-- MFC: Long dead, for masochists only.
-- WTL: never supported in the first place, requires C++ wizardry, and Microsoft's C++ track record is a joke.
-- .NET WinForms: Supposedly supported, but hasn't been improved for years. A dead-end for all intents and purposes.
-- .NET WPF: Looked really good but incomplete and slow. Windows 8 took it out to the back alley and quietly strangled it.
-- Silverlight: Officially dead.
-- Metro/WinRT: Also knowns as "Silverlight 6, tablet edition". Looks awesome, but it's nerfed. I mean that you can't use WinRT without also being restricted the "tablet app APIs" for everything. Will never be supported on XP, Vista, or Windows 7. That alone eliminates it as an option for the majority of desktop application developers.
So, what exactly are Windows developers meant to do now? All "legacy desktop" APIs are getting end-of-lifed either officially or unofficially, and the new WinRT replacement is so massively cut-down that it cannot hope to act as a replacement.
This is not an improvement.