I know this is a well discussed topic but I am late in the game of trying out the modern desktops and wanted to counter some of the negative reviews that have been published about Gnome3 in general and Gnome shell in specific. I have been sticking with Ubuntu 10.04 with Gnome2 for around two and a half years. It is only in the past few months that it became apparent that I really needed to upgrade my system.
I can easily boot to a test install that on my netbook computer and I put a copy of 12.04 on it. 12.04 defaults to Unity. I really do not like the Unity interface much at all. I won't go into reasons as they have all been covered by the numerous negative reviews over and over again, suffice it to say I agree with those reviews. I know there are a lot of people out there who do seem to like it, so more power to you - linux is all about choice, but it is not my cup of tea.
It took me a while before I got around to trying other variants of Gnome3. Because the reviews of Gnome3 originally had been mostly bad and I agreed with the negative reviews of Unity, I expected to not like Gnome3 at all. I happened to notice on my 12.04 test install that I had options to log into Gnome Classic and Gnome Classic (No Effects). I tried that out and pleasantly found a traditional Gnome menu that I am used to as well as familiar panels. The only real difference right off the bat was only having a close button on open application windows. On a netbook that isn't too bad but I can see how people wouldn't like it on a full sized desktop screen. But a quick search found that all you have to do is install gnome-tweak-tools and you can easily adjust the behavior to have the minimize and maximize buttons. So Gnome classic, with minor tweaks, is the look and feel of the Gnome that I had become used to with gnome2 but an upgraded version of Gnome with more configuration options. What's not to like?
Being inspired by a mostly positive first experience with Gnome3 I installed Mint 13 Cinnamon on one of my two desktop machines. The experience was great. After having used Gnome2 for a few years, it is a very familiar interface to what I'm used to but more polished, nicer looking, more configurable, more customizations, and some nice powerful features in the background. It is exactly what someone who uses Gnome2 would imagine that an upgraded version of Gnome would be like. Cinnamon comes across to me as the best user experience currently available in linux. I think new users being introduced to linux should be introduced to linux with a Cinnamon interface, let them try other desktops after they get hooked.
Didn't realize until after I started looking around for more Gnome3 articles and features that it is actually Gnome-shell that is the original default desktop for Gnome3. That option wasn't available for some reason on my test install so I went and put it up on my system. Again because of my negative opinions of Unity and the bad reviews that Gnome3 originally had I expected not to like it. I was pleasantly surprised that for a modern interface designed for netbooks and possibly touch screens it is intuitive and simple to use while still being functional.
Gnome-shell blows Unity out of the water. Considering that Gnome-shell exists I am surprised and disappointed that Canonical has chosen to continue to forge ahead with the Unity project. If they are trying to attract new users with a more modern simple to use interface they should be putting their time and effort into improving and integrating Gnome-shell. I would recommend to anyone who likes Unity, and especially anyone who made themselves sit down long enough with Unity to learn to like it, to give Gnome-shell a test run for a while. This is the best of the new style desktops that I have seen. I find it to be more intuitive and more functional even than Windows 8. On my netbook I often used the 10.04 Ubuntu Netbook Edition and I find it a little ironic that Gnome shell feels more like an upgrade to UNE than Unity does.
The negatives. I am quite impressed with what the Gnome project is doing and the versatility of what they have created, however there are some thorns. The main criticism I have with the new desktops is that they are a little slower than the older more traditional style desktops. Mostly I notice it when swapping out applications, when closing one program and opening another there is usually a distinct delay. This might happen in all desktops but it is more prominent in the 3D desktops. I have seen some machine specific glitches in winow behavior with the gnome-shell interface on the small screen my netbook. Windows not displaying correcty or having all features accessible. This hasn't been happing on my desktop with a large montitor using an Nvidia card. So there are bugs but they may only affect some users. Actually, even on the desktop computer gnome shell sometimes comes up with no panels, desktop only and I can't do anything - I have to log out and log back in again for it to come up correctly. I'd give a slight knock to the devs for making the default behavior of app windows to only have a close button. Considering that you haven't perfected the touch screen interface and netbooks are only a subset of the overall market that wasn't a good choice for the default. It is easy enough to configure though so that it is only a minor criticism.
KDE: I have always felt that KDE was the most configurable, most customizable, and potentially nicest looking desktop available. However it also consumes a lot of resources and ever since KDE 4 I consider it to be not very intuitive, taking a bit of a learning curve just to use to. I much prefer not to have to spend a lot of time learning just to do basic tasks on my computer. For someone who is willing to spend the time and effort to learn the system and to sit down and customize it, KDE is capable of being both such a good looking and functional desktop that it rivals anything the Mac is capable of. I hope KDE continues to thrive and be one of the top DEs around as they set the bar high for look and feel of the user interface.
XFCE: I have used XFCE in the past and it is a solid desktop with a traditional look and feel. However it is definitely old school and seems a bit limited and manual in customization abilities. For anyone who has performance problems with Gnome3 or KDE I would definitely recommend XFCE, or MATE, but if you have even a half way decently performing computer most people would be a lot more happy with Cinnamon. I still use XFCE some times as a fall back when speed is a noticeable issue for something I am trying to accomplish.
If you have a much older system or are having very serious performance problems then I would recommend LXDE. LXDE is a traditional but simple and straight forward desktop style that is light and fast. My netbook is not a high performing machine so I will often use LXDE on the netbook when I just want to get things done and the desktop experience isn't so important.
I had worried a bit about the future of linux after all the negative reviews of Unity and Gnome but after having tried Gnome3 and seeing how versatile it is in that it can be configured both with a modern small screen/touch screen style interface or with a more traditional look and feel of the menu system that most of us are used to there is some hope that we are still moving in the right direction. I do have concerns that the most popular distribution has chosen a desktop that isn't very intuitive and has serious performance problems when they could be putting resources into stabilizing gnome shell and making an interface that would really wow new users.
Cinnamon is definitely my favorite interface right now but I plan to kick the tires on Gnome shell for a while and see how much it grows on me.