I normally use XFCE, and I decided to try out Gnome about a month ago (with vanilla Ubuntu). I expected it to be stable and consistent and I would hate it for the UI design, since I wasn't a fan of Windows 8.
But actually using Gnome I find that it's the opposite. The window switcher in Gnome is amazing and the app menu is good, though I wish it could run commands like XFCE's whisker menu could (many times I need xkill and don't want to open a terminal). I dislike the lack of customization but honestly I don't find myself needing to customize so much since Ubuntu's default Gnome setup is pretty nice.
The thing that's surprised me most about Gnome is that it can be unstable and inconsistent.
- Sometimes Gnome randomly decides to run at 30 FPS and I can notice that my desktop feels sluggish. I have a high-end gaming PC so this is just unacceptable. I wonder if it's related to Gnome taking up more RAM than any other DE I know of.
- When a new window opens up, sometimes it appears and grabs focus, other times I get a message of "Files is ready" or similar, and it feels like it always does the opposite of what I want it to do (clicking "Show in file manager" in Firefox gives notification, annoying pop-up windows show up automatically though).
- The left panel's application list, when you have more than one window open, you have to hover to get the other ones, and it always shows them in order of last selected. I keep clicking on the bottom one, thinking "oh, that's not it, it must be the top one then", but the bottom has moved to the top so when I click the top one it doesn't actually change and I end up clicking through that menu 3+ times to get the window I want. This one is mostly just me being annoyed by the behavior.
- Yesterday I tried to delete a few thousand files in Nautilus, so I tried to use Shift+Click to select them, but that ended up causing all of them to open in VLC, which grab focus as each window opened, of course, (why isn't the "X is ready" feature put into place here...) so I couldn't click out of VLC. I eventually had to force power off my computer to stop it.
I do agree with Gardiner that KDE is buggy, but Gnome... I won't miss it.
P.S. Disagree completely with Gardiner on Adwaita light being good, especially when windows are unselected, the contrast is far too low for me, and there's also very little color in the UI which are really nice with light themes (this website, HE, uses color to accent the theme and it looks great, as do many websites). Then again, the (probably) most visited website in the world, Google's homepage, is too bright for me, so maybe I'm just biased. I use Adwaita-dark, both in Gnome and XFCE.