I have just recently switched from Cinnamon to KDE on Mint 17 and I am still discovering cool little stuff along with the odd quirks of KDE.
Kool KDE Features
The other day I had a cool moment with KDE, specifically with KDE Connect. I got an incoming call on my phone, and Amarok automatically paused for me to answer it, then after I hung up, the music automatically started again! Awesomeness! I assume it should work with other KDE media players, not sure about other non-KDE-native apps. It reportedly does work with Clementine. Some users have reported high battery life when scanning for a connection using Bluetooth, but I am using KDE on my workstation so I obviously cannot test that.
Another thing I love in KDE is it's System Tray not only shows all recent notifications but it also shows current file transfers for Dolphin, including estimated time remaining. Click the plus sign and it also shows the transfer speed too, which is very useful. You probably also notice I have switched back to Mint's default KDE theme.
Another thing I like is the "root actions" menu in Dolphin, which is useful for changing or repairing permissions on files and folders. I did not like Dolphin when it first replaced Konqueror for file management, but it has come a long way since the early days of KDE 4.x.
One mildly annoying thing with KDE is, and always has been for me, Kwallet. With my recent KDE use I have noticed it popping up when I open Chrome and Amarok for the first time after login. Luckily I found a little trick to stop Chrome needing to open Kwallet here without needing to completely disable Kwallet. I have not yet found out how to do similar for Amarok. Should I add a similar entry for Amarok? Answers in the comments please! I have tried disabling Kwallet before but it used to course problems, so I don't do that any more!
Another little quirk of KDE is the way it treats workspaces and monitors. It treats each monitor as a separate set of activities. The downside of this is you cannot set one widescreen wallpaper to span over two or more monitors. The only workaround that works at the moment is to edit your wallpaper in your favourite editor, I use GIMP, and split the picture down the middle and set the two parts to the appropriate monitors. I'll admit this is only a very minor annoyance but it means wallpaper switchers don't tend to work well unless you like different wallpapers for each monitor!
So far I am really enjoying KDE on my main workstation and I am still rediscovering the features and quirks of KDE, so I shall likely update this article in the future.