I'm looking at what will be 4.2 in a few months time and getting really, really excited about where we are going. It's not just Plasma, either, not by a long shot. For instance, KMail recently got model/view-ified when one of the Google SoC projects was merged. This was a huge step forward for getting KMail ready for Akonadi integration, but it also delivered a ton of visual and functional improvements in all the lists. The functional improvements include new threading and grouping models, message tagging, tabbed folderview (though I think it would make more sense to have tabbed message views?) and manual sorting in the folder listings. As for visuals .. well .. here's my kmail today:
This doesn't really do the new threading or header painting justice, but it gives a small idea.
Konsole's very useful find widget now appears inside the tabs, rather than outside of it, and supports session management. Amarok2 is looking really, really nice; the evolution its been through is impressive, but you really need to see it in action to get a feel for it. The animations and various interaction concepts just don't come through fully in screen shots. Okular's defaults are nicer now and the games continue to improve in look and feel.
KWin's compositing has gotten amazingly slick and smooth (at least with decent drivers; hardware doesn't need to be special, as I use it on a two year old integrated Intel mobile chipset in my laptop) and has simplified the configuration even further. The file dialog and file manager improvements in speed as well as features such as thumbnailing and what not have been consistently impressive as well.
Plasma has gotten more consistent and featureful as well. I especially like the little number beneath the arrow on grouped tasks:
The task bar now groups, does multiple lines and more. The systray allows icons to be hidden, takes care of notifications and lets us put non-tray-icons alongside the freedesktop.org ones. Visual continuity is improved, and we're tweaking the default theme (I'm personally hoping for a non-all-black panel) to make that shine even more. We have tons of new components, tooltips that are pretty and even animated (and which can be turned off globally; though no UI for that yet). New calendars and improved consistency for clocks. A better panel controller for configuration and visual drop areas for drag and drop just like 4.1 had for moving applets. Alternate interface support for KRunner, along with actions-on-matches. New applet handles, meters and other widgets. Improved scripting bindings, support for two new entire widget systems (you can see a screencast of the Google Gadgets on Plasma support here), wallpaper plugins, containment switching, extenders and .. well, just so much more than that even.
The amount of polish (ranging from big things like Kickoff's theming or how it's obviousl what the current or needing-attention windows are to small things like the new glow around the taskbar buttons that subtly fades in/out as you mouse over) and performance improvements (such as delaying wallpaper rendering of non-visible containments or the SVG data cache).
We'll all be polishing and improving many more things between here and 4.2.0's release in late January, but I'm already looking at what we have and thinking to myself, "What a wonderful world." I'm more excited about 4.2's fit and finish than I have been about any KDE release since probably 3.2, which was also a watershed release in terms of stepping up the game.