From a design standpoint, the new GUI is done really well. It's just the poor choice of defaults and the removal of certain features that make me wonder what's going on (and then there's the font rendering BS that I'm trying to forget). In any case, with a few extensions to bring back the removed features and some creativity, you too can have a very customized browser window.
note: the location bar is opaque in the screenshot for some reason, but it is in fact semi-transparent, so I can see Foxkeh.
I have my normal title bar, but not only was I able to hide the menu bar, I was even able to have the Firefox menu button. - https://addons.mozilla.org/en-US/firefox/addon/firefox-4-ui-fixer/
And oh yeah, the status bar! The new "add-on" bar is great, but not all add-ons have buttons that I can put on it. However, I can still have the old status bar framework for extensions that haven't been updated. - https://addons.mozilla.org/en-US/firefox/addon/status-4-evar/
Even got the dropdown marker for the back/forward button. - https://addons.mozilla.org/en-US/firefox/addon/backforward-dropmarker/
I thought Firesomething was finally broken (it hasn't been updated in several years - I remember using it in Fx 1.5), but the Ctrl+` hotkey gets me a new name.
Firefox 4 seemed to lack buttons that I had before, but I'm able to get a buttload of new buttons - https://addons.mozilla.org/en-US/firefox/addon/toolbar-buttons/
The only things missing are proper font rendering and the Phoenity icons that I love so much.