Have you tried the Dominions I demo? It lets you play all of the nations except the ones that are new to Doms II.
I think I can relate to being disappointed about the GUI, except that it's not really important to me. The Doms I GUI had a steep learning curve, and I got used to it. I think the Doms II GUI learning curve is a little bit less, thanks to more tips, but it is also different from the Doms I interface I'm used to, and doesn't really seem easier to use. Fortunately, I don't particularly care. I'm in it for the fun I have playing the game, and the GUI isn't a big deal.
The map and battlefield graphics are nicely improved in most ways. As for other parts of the GUI, I still actually kind of like the appearance of some of Doms I, in some cases, more than the equivalent Doms II GUI. I think the bitmapped graphics often look better drawn without the new 3D engine, for example.
To me, however, it adds up to two Versions of a game I really like, and for the most part, I'm very pleased with both. There are some things to fix and improve in Doms II, but there are even more fun new things to enjoy, and the devs are clearly interested in fixing and improving Doms II, so I'm quite happy about it all. What I really want now is lots more spare time, and the full Version of Doms II to arrive.
PvK