Not sure how some people can't get it in their heads that tactical combat doesn't need to be advanced. Bringing up Total War is the apex of poor analogies to those of us who actually like the idea of manipulating combat tactically. Total War is NOT designed to be a strategy game; that was an afterthought which has received a lot more attention in Empire and onward. Total War was built to be a tactical game that included a strategy element if you wanted something other than scripted battles (why else would you ever fight with spear militia when you could use armored sergeants instead?). A tactical game doesn't need to be an RTS-element (that wouldn't really make sense in GalCiv) and it doesn't need to be a very large element of the game, but it should have some effect.
I would personally vote for the limited control variant of tactical combat, i.e. something on the scale of Endless Space. Unlike some of the posters here who consider it a Rock Paper Scissors game (and I very much will dispute that point), I actually consider the idea of thinking about what I want my ships to emphasize in combat to be an important thing. With the Endless Space setup, you have to think about what you want, what the enemy will most likely do, and if the enemy counters your strategy what the best alternative is; beating the AI's card is often a very ineffective strategy in ES compared to simply using the one with the bonus you prefer. Its also very simple and still based on ship and fleet design over user input.
If nothing else, GalCiv3 needs two very basic options in combat: the option to retreat (which will also emphasize having FASTER ships, something I rarely cared about in GalCiv2 from a combat perspective; it also emphasizes having leftover movement points), and the option to pick priority targets (as the game's built-in targeting system can be gamed at points, such as by building large ships with minimal firepower but high defense and, say, a hyperspace booster, to prioritize that ship as a target). Most of my other problems with combat aren't tactical in nature; wanting carriers (even just a fleet-wide life support module), minimum die rolls for defenses and weapons (really don't want a 200 shield ship to get destroyed by a ship with 40 beam damage in 1 shot), and that sort of thing.