[Endoperez]

Some of the GUIs are just great. I love the Marignon one, it shows the whole 'sun above' in recruitment and nation overview, the streams of light can be seen in the info panel of the main screen, and the buttons in the left don't have any duplicate suns but the exit screen again shows the shine but not the sun itself. Very nice! Ulm is also quite good, and several suit the nation well (esp. Abysia). However, I don't like all of them, and many of them are too bright, straining my eyes if I would try to play with them on.

Also, I don't like Caelum's GUI, it really doesn't look like anything. Jotunheim's GUI is very good, but having a good picture of ice would be perfect for Caelum...
Mictlan's red blanket of a background doesn't work with their units. The green capes really stands out from the red. I don't know what would look good, but possibly some volcanic rock with red stains on it, or a picture of stone wall of Macchu Picchu or something.
Tien Chi's background would have to be refitted a little, so that the tree either is in left (not visible on the buttons on the left part of the main view) or looks like the same tree grows through the two button-groups.
Man's background is a very good idea, as Man represents coming of civilization, agriculture and fields. However, I think a field of more ripened to gold of autumn would work better if not made too bright. The green suits of the Tuatha in the theme have too little contrast with the background.
I don't really understand what Pythium's background stands for, and the fact the halo appears in both button groups and the info panel in the main view is slightly distracting.
Ermor needs a different background. Their units are all dark, and need a dark background or the details will be lost. Dark gray would probably do well, as it would help the dark purple of the Ermorian banners and shields to stand out a little. In fact, dark grey with skulls or "scream" faces embedded into it works quite nicely, but Gimp crashed when I was toying with different border options...
Machaka is just plain ugly. C'tis does't look like much, but at least it doesn't distract from playing.
EDIT: Pangaea and Vanheim seemt to have just random green and grey background. The green works for Pangaea, but it would still be nice if there was something better...