I really liked GalCiv2 except for one critical part of the whole experience. Tech tree on it was boring and pointless. Which was annoying since tech is my favourite aspect on any game in this genre. I seriously hope GC3 improves on this aspect. And I'm not just talking about lots of unique tech on races.
Multiple requirements, optional requirements.. Tech tree needs to be more complex. Or the very least it should support modding in tech tree that is more interesting and provides more options for advancement than just next in the endless straight line. Some techs should depend on more than one other tech possibly from other branches and some techs could have optional dependencies that are not required but could reduce research cost if acquired.
Other than that, I'm really exited on GalCiv3.