For part 1 go here.
Version 2.5 is easily the biggest update to the base game of GalCiv III since its first release back in 2015. What makes these updates possible is the continuing sales of DLC and expansions like Crusade.
The much beloved Galactic Civilizations II never got an update like this one. That is because back then, games were sold at retail and so there was no realistic way to keep updating the base game like we can today for budgetary reasons. Hence, GalCiv II came out in 2006. Dark Avatar came out in 2007. And Twilight of the Arnor in 2008 each being its own stand-alone game with the version before it being retired.
I don't know about you guys but I much prefer today's model where the base game keeps getting updated. However, developers often don't communicate the importance of expansions and DLC that make these updates possible.
Also, if you want to help us you can make a huge difference: REVIEW GALCIV III ON STEAM. If you've already reviewed it, feel free to write a new review. It helps reflect a more accurate recent review score. Steam uses the review score in their discoverability algorithm. Anything below 70% is basically invisible. Below 80% is mostly invisible (i.e. won't offer it on the search the store suggestions).
The main course
So far, version 2.5 (which we expect to release as an opt-in THIS WEEK) will have a number of immediate effects:
Changes the affect Crusade and GalCiv:
- Turn times are much faster
- The AI is much smarter
- Lots of bug fixes
- Massive improvements in game balance
Changes if you don't have Crusade:
- Crusade based UI
- Resources accumulate
Changes if you just have Crusade:
- You can, with a command line param, jump between the base game and Crusade
- When you play DLC that was originally made for the base game, the game can play it in base game mode for balance fixes.
- Crusade specific balance and fixes.
GalCiv III v2.5 vs v2.33
Let's take a look at some of the more obvious changes...
Setup screen
The setup screen is similar but with some key improvements such as the ability to mouse over an opponent and see what they are all about.
Main Map
Besides UI changes, GalCiv III 2.5 now starts with a Summary screen so you can see how you're doing compared to others. Moreover, you may notice that the graphics are quite a bit better thanks to the improved shading system.
Research Screen
Note that the technologies are no longer put into categories to sift through. Also, just a simple polish point, Professor Dawkins now asks you what you want to research.
Planet Screen
The planet screen is updated to show how much is going towards ship construction vs. social construction. Influence is now shown as a resource and now that food is a global resource it gets its own thing too. Word on the street (which will get tweaked to use that full area) now exists to tell you what people think of your planet.
Shipyard
Improved graphics and the ships are now animated (the colony modules spin).
Govern
The govern screen gets a make-over visually. Crusade introduces the Citizen-based economy. Coercion has been eliminated in both versions for 2.5.
Starbase Screen
Besides visual improvements, constructor spam is eliminated. If you have the resources/money you can build a module instantly.
Diplomacy Screen
The leader is now displayed rather than the planet. Minor races are no longer shown here but instead can only be communicated with via their planet and only if they are within sensor range (i.e. you need to keep a ship or sensor beacon nearby). In Crusade they are just speed bumps (though they will be getting a free update in the future to make them more distinct).
Trade Screen
The most obvious change on the Trade Screen is the barter bar. You can now see how close to a deal is based on how your opponents value each side's offer rather than guessing.
Next up
We hope you like what you see here! I'll be doing an AAR over on the Stardock Reddit. Feel free to join me there and subscribe. 
