By default it is an absolute nightmare if you're switching between multiple windows. Mate is fine and classic.
Overall I'm not completely happy with the desktop environment situation in Linux. I have high hopes for Cinnamon though and I think they'll nail it at some point in the near future.
EDIT: Wanted to ask, those who are using Mint: Are you using the "standard" release or LMDE?
GNOME3 has annoyed with with it's task switching too. I do like keyboard shortcuts, but task switching is horrible. Alt+Tab then down to switch between application windows; who thought that was a good idea? Then there is the virtual desktop situation...
You should try Xfce then.
I've been using Xfce for a long time, and I've always been satisfied with it.
I've never understood why people are so high on GNOME. It's never been good, and I always get a sand in the underwear feeling when I use it.
When I ran Mint for a couple of months, I used the LMDE. I was getting tired of 6 month release cycles, and I was curious about Debian after being in the RedHat ecosystem for a long time.
KDE leans heavily on the video drivers. If the video drivers aren't working well, you're experience will suffer.