Say what you want about Linux Mint - As of this moment, it's still an Ubuntu derivative, and both subject to Ubuntu's bugs, and reliant upon Ubuntu's packages. It owes a lot of its success to that of Ubuntu, but Clem and the Mint team are starting to really separate themselves from the groups they've forked code from (Debian, Ubuntu, and Gnome). The one, shining example of this is the continued evolution of the Cinnamon desktop.
I'm relatively new to the Linux scene, having just about 11 months of usage under my belt. I started with Ubuntu 12.04, then migrated to Mint 14 & 15. I did so, because Mint offered the same package structure as Ubuntu, but without all of the extraneous, bullshit flair that comes with it. Installation was just as easy, it supported my hardware, it was faster, and it was more stable. But during my period of use with Mint, I realized there was one overriding factor that drew me to it...the desktop environment.
Cinnamon is as clean as it gets. No frills, no fancy UI elements...it just works and looks great. You can tweak it, and theme it without the extra effort of downloading, extracting, and moving files into the correct places, the settings menu is clean, elegant, and has just enough options to be all-encompassing, without becoming cumbersome, and those options make sense. Nemo (the file browser for Cinnamon) is excellent - providing the user with necessary information, and nothing more, unless you want a little something extra. The color scheme is nice and vibrant, yet minimal and unobtrusive, which makes navigating the UI both easy and pleasurable. Shortcuts can be added to the bottom panel with ease, and are arranged in a way that looks stunning, without being gaudy.
Yet many Linux users rail against the Cinnamon project, and I don't really understand why. Cinnamon is everything a desktop should be, whether you're a power user, or a complete n00b. It's clean, easy to navigate, customizable, has a small resource footprint, and still remains powerful. KDE and XFCE both look like the cover of a Milton Bradley game box, with large, gaudy icons, UI's that require more mouse motion that is necessary, settings that are buried within settings, and require setup that many Linux users simply don't have the time and patience for. Sure, they may have more features than Cinnamon, but many users don't really care about extreme customization and tweaking. They just want something that looks great and works as expected.
KDE desktop
XFCE desktop
Gnome 3.10 is - in my opinion - an abomination of a desktop UI. The project is clearly being moved in a direction that will more readily support a mobile interface, and that's great...for mobile devices, but why oh why does the desktop unlock screen require an upward swipe of the mouse, versus a tap of the Enter key? If the Gnome team want to move into mobile, I wholeheartedly support that, but they're going to need to rethink their approach a bit. One UI for mobile, and one for desktops...it's really not a difficult concept to grasp.
The Gnome lockscreen looks nice, but isn't suited for desktop use
Cinnamon is everything these desktops are not. It looks great out of the box, and you don't need to spend 14 hours tweaking it, to get it to look and work the way you want it to. Clem has not burdened himself or his team with the mobile rat race that Gnome and Ubuntu are in, and I think they're reaping benefits because of it. Mint is #1 on the DistroWatch top 100 list, and I think Cinnamon is the main reason why...it looks great, and people love it. In fact, a lack of Cinnamon compatibility nearly prevented me from installing Arch Linux. I ended up scouring the web for information, and found out that Cinnamon 1.8.8 (updated to 2.02 today) was in the AUR, and haven't looked back since. Now I have a great Linux distribution, built the way I want it - no extra preloaded or proprietary crap - and I can run Cinnamon.
My Arch Cinnamon desktop
This is, of course, simply my opinion; If you enjoy Gnome, KDE, or XFCE, keep on keepin' on. I don't hate those DE's at all...I just feel that they look hideous out of the box, and require too much effort in order to obtain the kind of look that I enjoy. They are, however, the old guard of the Linux world. They've been around forever, and many long-time Linux users have settled on one of the three. That's fine...Just don't flame me for wanting something a bit more refined, and a little less high maintenance. To each his own, but I truly believe that a DE like Cinnamon is 1) what people want, and 2) the kind of DE that will attract new users in droves. In the end, I think the Linux world will see a shift in the way desktop environments are made, and I believe Cinnamon will be at the vanguard of that assault. Cinnamon provides the best combination of user-friendliness, aesthetics, power, resource consumption, and customization, currently available - That's what makes it the best DE for Linux.