Let's start this off with a brief review of what Linux Mint Debian Edition (LMDE) is and what it isn't, followed by what this release is and what it isn't.
LMDE is a Linux Mint distribution, containing all of the nice Mint tools (installer, updater, menus and other utilities), plus lots of preloaded and preconfigured packages, but built on top of Debian GNU/Linux, rather than Ubuntu as the numbered/named Mint distributions (currently 14/Nadia).
Specifically, it's built on the Testing Branch of Debian — currently the 'Wheezy' release (although probably not for much longer). There are pros and cons to this - if you don't like Ubuntu, or you really prefer to start from a cleaner, more basic distribution, then being based on Debian is a big plus.
On the down side, it means that it contains a lot of things which are well behind the latest current releases, starting from the Linux kernel itself — 3.2.0 rather than the 3.7.x or 3.8.x that other recent distributions feature — and the X Window System, 1.12.4 compared to 1.13.x, and so on.
What this means is that you need to pay a bit more attention if you're going to try LMDE, make sure your hardware is compatible and supported, and be prepared to put in a bit more effort in getting everything installed, configured and running. The fact is that pretty much describes a typical Debian user anyway, so I don't see it as a big problem.
LMDE is a 'rolling release' distribution, so this release is a roll-up of the updates which have been made since the last set of ISO images was released, it is NOT a huge leap forward packed with a new kernel, new utilities, new applications and such.
In fact, LMDE is a bit of an exception even in the world of Linux rolling release distributions, because by default LMDE does not update continuously: instead, updates are collected into bundles, which are then released as 'update packs'. (This new release comes with update pack 6 included.)
The advantage here is that it reduces the chance that an update will have negative side effects and break something (or everything); the disadvantage is that it can seem like a long time between update packs. So long, in fact, that for things which are commonly used and frequently updated, such as Firefox, separate patches are issued independent of the update packs. (If you prefer a more typical rolling release model, you can use the LMDE "incoming" repositories.)
The release announcement for the 201303 build gives a good overview and summary of this release. One thing that is important to note there is that it explicitly states that there is no EFI, GPT or secure boot support. So if you have a UEFI system, you can only install LMDE via Legacy Boot, if your BIOS supports that option. Even in that case, though, the other limitation is likely to bite you because as far as I know, the majority of EFI systems also have GPT partitioning (perhaps all?), so what is likely to happen is that you switch to Legacy Boot, install LMDE, it looks like the world is going to be a wonderful place, and when you try to reboot after installing it fails with a complaint about not being able to load the kernel. Does this sound like the voice of experience talking to you? Well, it is... the bottom line is, if you have an EFI boot system, and you do not have strong masochistic tendencies, you probably don't want to try to install LMDE on that particular system.
Of course, the other major thing that LMDE gives you is a choice of desktops. There are ISO Live images for Cinnamon and MATE (with 32-bit and 64-bit versions of each of those). I installed the Cinnamon version on most of my systems:
But on one of my netbooks (the Samsung N150-Plus), I installed the MATE version:
Other than the different desktops, the rest of the content of the two versions is the same. Some of the highlights are:
Linux Kernel 3.2.0
Cinnamon 1.6 / MATE 1.4
Image Magick 6.7
Banshee Media Player 2.4
Totem Movie Player 3.0
Another major advantage of LMDE is that it is 100 percent compatible with the Debian Testing repositories. If there is something you want or need that is not included in the base distribution, your chances of finding it and being able to just download and install are very high.
So, to return to the opening paragraph, how do I summarise Linux Mint Debian Edition in general, and this release in particular? In rather loose terms, I would call LMDE a Linux devotee or hobbyist distribution. As it says in the LMDE release notes, "LMDE requires a deeper knowledge and experience with Linux, dpkg and APT".
If you're new to Linux and don't have that knowledge but would like to learn, LMDE is an excellent place to start — but don't expect it to be as complete, polished and user-friendly as the Linux Mint Ubuntu-based distributions.
As for this release, if you already have LMDE running all you need to do is make sure that you have update pack 6 installed and it will be the same as this release - there is no need to reinstall this. If you're installing a new system from scratch, though, you will definitely want to use these new ISO images.