What are the reasons to be unhappy? I bet most of you would guess. I'd just like to add that there's substantial difference between KDE 4.0 and GNOME 3.0 release and that is — while KDE 4.0 was just premature release, GNOME 3.0 is broken by design. No amount following minor releases can fix that. Yes, most of the changes to GTK 3.0 are good and enable people to work with this toolkit in a better way, but that's where GNOME 3 goodies ends. Unless you want a highly usable open-source software for tablet, Gnome 3 probably isn't for you.
And as Fedora 15 Alpha is behind the doors it's a good opportunity to try out other desktop. If you liked Gnome 2.x series you're probably left up with two options: KDE, which finally matured to be feature complete again, and XFCE which is steadily becoming better. LXDE seems poorly maintained at the moment so I wouldn't recommend it. And of course, if you, in addition, want a gtk based desktop then XFCE is the only option (right now).
XFCE is surprisingly configurable and with a bit of effort it can be turned from ugly duckling to pretty (and usable!) desktop. Say, would you guess the screenshot bellow is actually XFCE?
OK, I agree, it's not as mature as KDE or Gnome 2.x series but I guess if enough of us put our money where our mouths are we could accelerate its development considerably. As a starter, let's identify the issues ;-)