I can't stress enough that this is a release candidate version and not the final version that will appear later this month, and these are just my initial thoughts after sampling the 3 default desktops that come with Linux Mint 12. I have every confidence that what will appear later this month will be more polished.
OK, having said that, with Mint 12 and everything that has gone into making Gnome 3 usable, Clem and his team really had an uphill battle. And they have made Gnome 3 usable. It does not have the customization or the user friendliness of Gnome 2, but they have given the Gnome 3 pig a complete makeover rather than just applying lipstick.
The MGSE desktop above has workspaces on the desktop, and it shows minimized windows. It has the Mint Menu on bottom, and the little infinity symbol at the left top opens the Gnome 3 desktop with its weird one-window design. MGSE is usable, and will likely improve with time.
What I don't like about MGSE: I can't seem to enlarge the text on the top panel, you almost need a magnifying glass to see the clock on my netbook. And the icons are spread out, and badly uneven in size. Most of my problems with MGSE so far are cosmetic. Last night sporadically when I would click on the Mint Menu my desktop would disappear for a few seconds, but that is a bug I expect to be soon fixed.
As I said, MGSE is usable compared to Gnome 3 Shell, and while not likely to please everyone, it is better than a number of alternatives.
To get to the other desktop options in Mint 12 you need to log out, then click on that cog-like icon, and log into your choice of desktop. Right now my favorite choice is Classic Gnome.
A couple of reasons why this is my choice desktop for Mint. First of all it took me just a minute or so to configure it as I wanted it to look. I just needed to drag and drop my favorite apps onto the desktop, and then move them where I wanted them. (Note that you cannot do this in MGSE. You must click on the infinity symbol on the upper left of the desktop then add apps to favorites by right clicking on them, but I found no way to actually add apps to the desktop or panel in MGSE). Also it needed but a right click on the workspace at the lower right corner in Classic Gnome to add a second workspace, though I could have added more than that. And I find the clock and text on the Classic Gnome large and readable, which I prefer. From what I've seen so far, this is likely to be the desktop that Gnome 2 lovers are going to feel most comfortable with. There is the caveat that this Is Not Gnome 2, the Gnome developers have done a good job making it harder to configure the Gnome desktop overall, so keep that in mind, also keep in mind that this Classic Gnome desktop choice only exists as long as the Gnome developers decide to allow it to, and my confidence in them doing anything smart or useful is in the low single digits percentage-wise.
This brings me to MATE. My first impression of MATE was that I liked it. It reminds me an a whole lot of Lubuntu (LXDE) desktop.
The problem with MATE is that it is so unfinished. My volume control would not work, there is no volume icon on the panel, no battery indicator on the panel either, and if you look closely at the screenshot above you will see that the Wireless icon is running off of the bottom right corner of the page. I added the workspaces by simply right clicking on the panel, choosing add, then workspaces. But there was no choice for adding the volume or battery indicator.
I think MATE will improve in time, but it is clearly unfinished at present, and it does not have the polish of Classic Gnome, for instance, the font rendering is not as good in MATE as it is in Gnome and Gnome Classic. Also Mate froze up on me while writing this so that I had to restart the computer.
Some early conclusions: Again, this is a release candidate that will have more polish and bug fixes by the time of the formal release later this month. But from what I have seen so far, I would have to say that Mint 12 using the Classic Gnome desktop is the most usable for me. The MGSE desktop is a somewhat close second choice. But MATE I'm afraid is just too unfinished to satisfy those Ubuntu/Unity and Gnome 3 refugees. I think they are going to be happier with MGSE or Classic Gnome, either of which is a matter of simply logging into their choice in Mint 12.