Hi,
When I first upgraded to V14, this was the first thing that I ran in to. After using it a while, I found that if I hit the little [-] button at the top of the tree part of the view, and just ignored that panel that it felt better, but I still missed the old panel layout. These days, I leave the tree view expanded, but rarely use it. With the new open completion functionality, it's usually superfluous. I type partial file names in the edit control and select from there, or explore by clicking ".." or folder names, or I type relative paths in the edit control.
One caveat to typing relative paths that I found is that given this structure:
A\B\C
with the CD being in B
typing C\ shows the contents of the C folder in the panel.

Typing ..\ does not show the contents of the A folder in the panel.

Typing ..\B\ does not show the contents of the B folder either.

(14.0.2.2 win7 64bit)
-Tyler