I've been using MATE on Fedora Linux for years, and gnome2 before the gnome3/shell silliness happened. Fedora Linux has been my primary desktop OS since 2008. I keep 1 laptop with Windows on it for those situations where I really need it, but other than that, I've been MS-free for almost a decade.
I think Windows still shines as a desktop OS in 2 areas:
1) Outlook : still seems critical for those in the corporate world. for me, i've gone with thunderbird plus various extensions to sync my contacts and such with Google cloud stuff and i haven't regretted it nor missed anything from my days using Outlook. everyone's use-case is different, so I can see how that might not be sufficient for others.
2) Games : gaming on linux has gotten a lot better, both native games or via wine, etc. but it seems Windows is still the primary OS platform for most PC games. as i'm getting older and priorities shift to family and other things, i don't miss it that much honestly. but i can see how this would be an issue for some.
I mostly use MATE for my desktop environment (+compiz+emerald), especially when I need to be productive. I play with Gnome3 just to see how it's progressing, but I still find it frustrating when I just need to get work done and find myself switching back to MATE. I've switched to KDE a few times in the past, and it is fine and all, but I have a personal preference for MATE now (which use to be the other way, i think MATE/Gnome2 has matured a lot). I occasionally play with Enlightenment, as that was one of my favorites back in the early days of desktop linux, but hasn't stuck with me. My friends keep telling me I'll really love xmonad, but then again those are the same friends that love Gentoo, which I find to be unproductive mental masturbation.
Glad to see others finding Linux as desktop OS usable...