Caesar in Gaul fails to make any meaningful attempt at recreating the actual campaign of Caesar. That is the real purpose of a mini-campaign, to be a focused map and a focused campaign based around these historical wars. As just a sandbox, it plays no differently than the base game.
The technology trees are at times lazy and poorly designed. Multiple turns per year advertised as a meaningful feature, as with seasons and attrition. TPY, seasons and attrition all should have been part of the Grand Campaign.
The Caesar tree focuses on Imperium, which is largely an unwanted effect in this campaign specifically because of the unavoidable Gallic Uprising at maximum Imperium. As well, most of the technologies aren’t anything worthwhile, while other parts are quite valuable. (ie. Elite “Legionary Equipment” and “Befriend Gallic Chieftains” are fantastic cost-saving moments, but “Appoint Legates” and “Bribe Gaius Scribonius Curio” are counterproductive at the best of times, serving to pump-up the unwanted Imperium not as a counter-measure to the player but because CA don’t seem to understand their own mechanics.
The Crassus tree is actually well done, with commerce being the focus, the bonuses being large enough to validate the overall cost of that branch of the tech tree. There is nothing special about it, nothing that meaningfully reflects what undistracted support from Crassus would mean. He was more pliable than Pompey and a lesser rival, being in his old age and not having long to last.
The Pompey side of the Roman tech tree is weird, with articles such as “Promote Hispanic Claim” which provides Level I horses and decreases unit cost, but it does not explain where those horses are from (though it can be assumed they’re imported from Hispania, nothing is said in the description of the quality of Iberian horses). Likewise “Banquet for Julia” is a meaningless tech tree that costs a hefty 4000 and offers a measly 4% decrease in unit cost and +4 public order from Latin culture. For “Support for Pompey”, you often only get a weak decrease of unit cost to some unrelated event. “Return Legion”, as the end of Pompey’s tree is nonsense. The loss of Pompey’s legion was a big deal and an intentional move to ruin Caesar, but there is nothing reflecting that via this technology. How about a large boost in one area, while resulting in the loss of allowed Army power (ie. reduction to 15 or 14 Armies allowed from 16 at Maximum Imperium)? There are better ways to use these characters and events, Pompey was his principle ally and rival.
As for the Barbarian factions, their tech trees are reshuffled versions of the Grand Campaign to fit the timing and theme of the campaign, which is acceptable. Though the pay-for-tech system leads to situations of unreasonable cost for little in return.
The Gallic Uprising and Roman Escalation are broken, the former being absurd and rendering the game to a standstill and the Roman AI completely failing to use the latter.
“New units” introduced in this should have been in the base game at release, in the case of Chosen Swordsmen, Chosen Spearmen, and Gallic Hunters (playing Arverni previously was much more dull and stark, without midtier units). The Mercenary and Auxiliary types introduced also seem like things that should have been in at release.
Massilia now being made playable in GC, they should have been “unlocked” in CiG, as they would have provided a unique start and roster. A near-Iberian and Briton faction should also have been playable, as they would similarly open unique starting points and varied rosters. The historical battles introduced are weak, and do not compare at all to the well scripted and impressive battles of Shogun 2.
There are also small details missing, such as the withdrawals of Pompey’s Legions from Caesar (the technology for it is meaningless), Caesar’s use of/access to Cretan Archers, etc. Reduced what could and should have been reasons to have trade nodes into technologies (ie. getting resources through technologies in a broken and forced tech tree, instead of actually trading to acquire them using nodes).