The desktop environment (DE) that I've been using since I started using Linux is GNOME. Currently, with Linux Mint 7, I'm using GNOME 2.26. I really like GNOME for its simplicity, its lightness on RAM, its great collection of applications, its customizability, and its stability.
However, I took one look at some screenshots of the newly released KDE 4.3 (really, 4.3.2) and I was instantly smitten. I decided to try it out, so after configuring the proper repositories (the Ubuntu/Kubuntu 9.04 repositories don't have KDE 4.3, only KDE 4.2.2), I went ahead and installed it.
First, let's have some history (or, at least, what I remember off the top of my head; you can verify this information in Wikipedia by looking up the articles on "KDE" and "GNOME"). KDE was actually the first DE for the GNU/Linux project. It started around 1996 alongside the development of the Qt libraries. However, around 1999, issues arose over KDE using the non-GPL Qt libraries, so a group of KDE and Qt developers left and started GNOME and the GTK+ libraries.
Now comes the actual review on my 2004 Sony VAIO desktop with a 2.8 GHz Intel Pentium 4 HT (single core) processor, 1 GB RAM, and ATI Radeon 9200 graphics card.
My first impression after booting up and logging in (I haven't bothered to change the login screen from the default Mint 7 "Dew" theme to something more KDE-like) is that KDE takes a bit longer to load than GNOME; it almost takes as long as Windows XP on my computer. This may be because of KDE's higher level of polish and greater number of features, but in any case it is slightly but noticeably slower than GNOME.
Next, I played around with the Desktop a bit. The first startling revelation is that the contents of the Desktop aren't shown on the desktop; one must either open the Desktop folder in one's favorite file manager (more on that later) or create a nice snazzy Plasmoid (yes, that's the name for widgets in KDE 4's new Plasma desktop manager). The Plasmoids themselves are quite nice looking and functional, though the weather Plasmoid is rather lacking in information (it doesn't even have a forecast!). The way to access Desktop icons without opening the folder is to create a Lancelot Part Plasmoid and drag and drop the Desktop folder into the Plasmoid; this will create a permanent housing for the Desktop folder's contents. However, clicking on any file or folder in the Plasmoid will reopen the file manager rather than create a new Plasmoid.
I was intrigued by the new "Social Desktop" Plasmoid (one of the more talked-about features in KDE 4.3) until I found out that this did not mean that I could use Facebook from the Desktop without opening a browser. The "Social Desktop" is its own service (for KDE 4.3 users), while the Facebook Plasmoid itself doesn't work. That's a moderately large letdown right there.
The menu works very nicely; the layout is slightly different from the default MintMenu, but it is intuitive enough.
One quirk I found is with the virtual desktop management. For some reason, even if one switches to a different virtual desktop, windows in other virtual desktops remain on the panel. It doesn't seem buggy, but GNOME actually keeps applications minimized to a panel in a certain virtual desktop in that virtual desktop when the virtual desktop is switched. This greatly reduces the clutter on the panel.
One bug I did find was when KDE's panel (formerly Kicker) crashed on me twice on the same day. This is seriously buggy behavior and frankly unacceptable. I have never had a problem even close to this in GNOME.
One thing I like about GNOME is that it integrates Qt (KDE libraries)-based applications very nicely. Sadly, the reverse (KDE integrating GTK+ (GNOME libraries)-based applications) is not so true. Yes, GTK+ applications still work in KDE, but when running, they look like one is running Windows 95. It's a big disappointment aesthetically, considering GNOME completely carries over the Qt-look from Qt-based applications when running in GNOME.
This extends to even non-GTK+-based applications like Firefox and OpenOffice.Org. It's especially bad in OO.O as all of the icons turn into boxes of text, hiding half of the menu bars due to the long boxes of text. KDE probably wants one to use the native KOffice, even though this isn't even installed by default with KDE 4.3. Even worse, KOffice has much worse feature, font, and cross-product/file type compatibility support than OO.O. This is probably also why GNOME doesn't force AbiWord and Gnumeric on users by default except on lower-end distributions (and even then, AbiWord and Gnumeric have much better support for features and cross-software compatibility than KWord and KSpread). This isn't as much of an issue in Firefox, but GNOME integrates Firefox much better than KDE does. KDE probably wants one to use the native Konqueror browser (though it doesn't even come with KDE 4.3 by default), but GNOME doesn't usually require the native Epiphany browser like this; furthermore, versus Firefox, in terms of customizability and proper rendering of pages, Konqueror is on par with Internet Explorer 5 - it just isn't there.
One very bright spot is the selection of games (not real games, just diversions a la "Solitaire"). The selection of games is much nicer in KDE than in GNOME, and I would definitely play those just to keep myself busy for a few minutes when not doing something else.
The other, more important, bright spot is the file manager Dolphin. Nautilus (GNOME's file manager), take note. Dolphin has a lot more support for different types of viewing, like Mac OS X Finder-style split-pane viewing combined with tabbed viewing. It has a preview pane which allows one to really see a big (not tiny) preview of the document in question before opening it.
I will be keeping KDE 4.3 on my computer, but after spending a week with it, I'm ready to go back to GNOME. There are simply too many compatibility issues with non-Qt-based applications to continue with KDE, and the speed and stability isn't really what I'm used to from a Linux system. That said, I will still use Dolphin and all of the neat KDE games (in GNOME), but I will wait to truly switch to KDE.