I agree with you that people shouldn't always expect things to be simple with no learning whatsoever. But every major desktop operating system has some concept of an app launcher that is generally very simple and intuitive to access. Being able to figure out how to access that or get back to "home base" shouldn't require any training. That's a pretty major flaw in my opinion.
Also making the app launcher (metro) a modal window that covers up all of your work is idiotic on a PC. It's a tablet convention, there's no need to cram it down our throats when we're on a PC.
Criticism of the OSX version of Finder was widespread and harsh. Criticism of Ubuntu's new interface has often been similar (not to mention The Ribbon). Heck, if one went by comments from command line gurus here on HN, it might seem as if the utility of GUI's for widespread deployment was still an open debate.
The integration of the Metro interface with the desktop PC requires a paradigm shift, but in the long run it will probably prove better to have done sooner than later because of the benefits it affords developers directly, and thus users indirectly.
I think their valid points and I like seeing Microsoft really going out on a limb. There's just something about the app launcher taking over the entire screen that feels wrong on a PC, though.
If you were to pin all of your main apps to the task bar then conceptually it's not too far off from the OSX dock plus launchpad concept. I really find no use for the launchpad on anything but a tablet so that's probably why I feel the same about Metro.
Also making the app launcher (metro) a modal window that covers up all of your work is idiotic on a PC. It's a tablet convention, there's no need to cram it down our throats when we're on a PC.