So, I've been watching YouTube videos of ship combat from other 4X games, and they look suitably epic for space settings with massive fleets on both sides being visible in the same frame. By contrast, GalCiv3's battle viewer feels like it pales in comparison.
Part of it is because the battle viewer may have various camera options, but none that's centred around the midpoint of the ongoing battle at a 45° angle. The best you can do with it is the "Top Down" view - which makes both fleets look like pieces on a chess board more than anything - or the "Free" view, which is finicky to control at best.
For GC4, you guys should take a leaf from - yes, gonna have to go there - Stellaris. Take a look at this to see what I mean:
I know, the battle itself looks like a right tangled mess, but you gotta admit the angle of the camera is better than the one we currently get with GC3.
Hell, we don't even have to go that far afield; you can look closer to home, and take a leaf from Sins of a Solar Empire instead:
GC4 ship combat should hopefully look more similar to these.
On another note, please overhaul the entire Trade mechanic.
Currently in order to build a Trade route, I have to design and build a freighter ship that I would otherwise not have cause to build very often at all.
In fact, my freighter may not have enough range to get to the planet of the other race that I want to trade with. Which means I have to research Support modules and build Starbases to extend the range sufficiently such that my freighter can reach its destination.
Also, which planet in my empire should I build my freighter from, and which planet on the other side should I choose to send it to? It's not at all clear how the choice of one planet or another affects how much profit I can stand to make from the trade route.
Lastly, once the trade route is established, I get... what's practically peanuts compared with my other sources of income, such as Wealth buildings and (especially) Tourism.
It's a helluva lot of effort for not much in terms of payoff, is what I'm saying.
How about simplifying the whole thing by folding it into Diplomacy?
You could research a tech that allows you to set up a Trade Treaty with another race, much like the other types like Exploration, Non-aggression etc. etc.
Once you set up a Trade Treaty with another race, it could be represented by a trade route linking the Capitals of both races.
You could then make it such that freighters are automatically produced and controlled to move back and forth along the route, just like it worked in GC2.
Or to make it more interactive, you could allow players the option to build Freighters from any of their Shipyards, which would then automatically move along the trade route as well. How much you profit from the trade route is based on how many Freighters you can build and send on it, and it gives you a reason to build a Hypergate lane across the trade route so your Freighters can benefit from it as well.
It also gives more possible options on the Diplomacy front. For example, you could make Trade Sanctions a thing that players can use.