I 
really like the new GUIs; they're great!  I won't start a new game without them 
 
Some comments on the GUIs:
Abysia:  Great!  Might look better with a border, though.
Atlantis:  Great!
Pythium:  Perfect!
Man:  Great!
Ulm:  I like it, but it's a little high-tech, and a little busy.  Makes me feel like I'm playing Total Annihilation on Metal Heck.
C'tis:  Perfect for Desert Tombs.  It's probably not possible to do a different gui for the Desert and Swamp themes, though 

Arco:  Very pretty.  A sky theme is appropriate, but...  if it was possible to change the text to white (which it probably isn't) then a night-sky starscape would be perfect.  However, if the text is black, that's not possible.
Caelum:  Really nice!  It looks a little bit "blue" and watery, though.  I brightened it (increased gamma, brightness, and 'green' level), and it looks more icy.
Ermor:  Very thematic, but... a bit too busy for me 

Marignon:  Nice, though a bit plain.
Pangaea:  Looks a bit like green marble.  Something a bit more 'foresty' might be better - with leaves and / or bark, for example...
Vanheim:  Very nice!  A little dark, though (for the text); I thought it looked better with an increased gamma, brightness, and blue level (makes it look colder).
Jotunhiem:  Very nice!
Ryleh:  Nice, but needs more tentacles.  Just kidding 

Mictlan:  Nice!  Dark like blood, yet does not reduce legibility.
Tien Chi:  Very Oriental...  BUT...  it really interferes with reading the text.
Machaka:  Thematic, but also a little too busy (hard to read the text).
These are just my opinions, of course, so don't feel compelled to change anything if you like it as-is 
