Tactical combat? Depends on the game’s goal. If it is to be a Empire game then Tactical anything (from the leaders point of view) is really unrealistic micromanaging (if you where a hive mind I would have no problems with this) Though the time and scale problems are still there (macro managing a Empire over months or years at a turn and then micromanaging a comparatively small tactical fleet battle over a coerce of hours or a day?)
But if we are to have strategic and abstracted battles we also NEED AI commanders that can intelligently handle the job and options to be able to change strategic and in turn Tactical decisions. For example allot of Tile based war games use abstracted numbers for attack and defense but they also tend to have other factors like moral, additional attack and defense number vs certain types of attacks, special abilities, abstracted formations (additional bonuses and penalties vs. attacks and defenses), disposition from aggressive to aloof) etc. etc . . take these with terrain and other factors and you get a complex and enjoyable strategic war (not just battles) this is what I miss in GalCiv.
I would like more diversity of technology, races and abilities. A tall order but has been done in other games. (see SEIV)
Real exploration and interesting finds . . some mundane and some spectacular . . There should be 100s or more allowing the possibility of finding something new in successive game and not just in one game. (this would be also a great way to use fans as a resource.)
A sense of galactic borders. Borders (and resources) are what most wars are about so having them in some sense would be good. It would even be good to have a overlay of what you think is your borders and what others think . . the overlap is contested . .
A way to make most colonies useful. In most games only the very developed colonies are really useful. In some games special resources or other factors can make a colony useful . .but also I would like to see trade within an empire . .Raw materials from outposts or rural farming planets being shipped into the “core” to be processed and some of that in turn shipped back out for expansion. Lose of these “less important” colonies could cripple the core.
More diplomacy so far most diplomacy has been picking items from a menu to ask for things you want. I would like to see a game that made diplomacy with another empire very hard but very rewording if done right. Some things that would help are (translation tech slow in becoming perfect, translation problems – good and bad, cultural differences, prejudices, personalities, exec . . and portrayed dramatically) these have been done in other games . . but it is not very common in these for whatever reason.
Some more real trade between empires and cultures with more possibility for profit and loss. Some smaller empires would be better at exporting raw materials to over developed large empires . .this make the trade vital for both and can be fun to play with to maximize your export and profit while hindering the others (peacefully). Small empires can become very important then . .
Etc. . .