The GTK-Toolkit changed it’s default file chooser dialog to a new interface which seen rather controversial. It is not a rudimentary as it looks, though.
Important Bindings
- C-l
- Open a location bar which uses completion and is generally helpful.
- /
- Open the location bar at the root directory (just as in Emacs

- ~
- Open the location bar at your home directory (again, just as in Emacs

- M-up/down
- Up or down one directory (down to a previously visited directory, not the selected item in the list).
- M-home
- Jump to your home directory
- M-d
- Jump to your desktop directory (e.g. ~/Desktop)
- M-1..0
- Jump to one of the bookmarks
And there is a right mouse context menu which let’s you toggle the visibility of hidden files.
Customizing
If you want to use the old file dialog set
(setq x-gtk-use-old-file-dialog t)
See also the variable ‘x-gtk-show-hidden-files’
Documentation