I bought the ultimate edition from Steam a few months ago, and have only JUST found out that:
1. You do not need to have the Steam client running to play the game. Instead, you could go directory to the galciv2 folder and run the game .exe from there.
2. Not only that, but you could play the vanilla Dread Lords (\GalCiv2.exe) and Dark Avatar (\DarkAvatar\GC2DarkAvatar.exe) too, not just Twilight of the Arnor.
I wonder if these have been mentioned elsewhere, but I think it should be made better-known. With all those complains floating around forum about TA breaking the AI, I was quite keen to have the DA available for trying, and this is quite a pleasant discovery.