The campaign civilisations feel outdated now.
2/3 civilisations (Malta and the USA) from the vanilla campaign were added to the game as regular civilisations now.
In half of the TWC your essentially play the USA too.
Age of Empires 3 (Vanilla)
Act I: Blood
The Malta civilisation is kinda modelled after the campaign already so not that much should be changed.
Units
- Fire Throwers replace Hoop Throwers
- Hospitaler replaces Rodelero
The Fire Thrower is a way more well rounded unit then the Hoop Throwers. It might also be confusing to new players that those units look the same but function differently.
The Sentinel should not be trainable because it’s a code design on this civilisation to not have a Musketeer or Dragoon unit because you are supposed to mostly use archaic units.
Home City
- Hoop Thrower and Rodelero shipments get replaced
- Sentinel shipments added
Other changes
Voice lines get replaced by Maltese ones.
Flag gets updated to the Maltese one (the one they use in the campaign is Medieval)
Units like Sentinels could appear as non trainable units in some missions or cutscenes.
Act II: Ice
John Black’s mercenaries are mostly resembling Germany so not much need of a change, but we have a second Mercenary civilisation with Sweden now so why not add some of their features?
Also the Haudenosaunee are a playable civilisation since TWC and they play an important role in the story.
Units
- Carolean replaces Musketeer
- Forest Prowler replaces Skirmisher (maybe after the “The Rescue” mission)
Home City
Some of the cards get replaced with the Swedish Contract cards that allow you to train those mercenaries in normal buildings.
Other Changes
The “The Rescue” mission could be reworked by adding a War Hut and a Corral to the Haudenosaunee village instead of a Trading Post.
The Tavern could be added to the civilisation and each of the missions could have mercenaries that make sense to be there.
Act III: Steel
You play as United States in this campaign but you aren’t really representing the US government/armed forces but more like a private company so Units like Regular or State Militia make little sense.
Units
- Carbine Cavalry replaces Dragoon
- Gatling Gun replaces Falconet
- Sharp Shooter replaces Skirmisher
- Sloop replaces Cavarel
- Steamer replaces Galleon
- US outlaws in the Saloon
Home City
Units get updated and the specific upgrade cards for them too.
AI factions
Mexicans are replaced by actual Mexicans.
Musketeers or Peru get replaced by Peruvian Guards.
The allies in the “Lost City of the Inca” are replaced by the actual Inca.
Other chances
Manors get replaced by normal houses.
The WarChiefs
Act I: Fire
This is a bit tricky as you play the US before it’s independence here unlike the US civilisation.
You get Revolutionaries in this campaign but unlike the normal Revolutionaries they are Skirmishers which is confusing to new players.
Units
- Revolutionaries are turned into Musketeer type units and replace Tomahawks in the second half of the campaign
- Revolutionary Sharpshooters (from the US Revolution) replace the Forest Prowlers in the second half
Enemies
The British can train Rangers.
The Skirmishers in all missions are replaced by Rangers.
Hessian enemies could use some of the new units from the Royal houses and Giant Grenadier Mercenaries.
Act: II: Shadow
Units like Musketeers and Skirmishers feel really outdated in this campaign and should really be replaced.
Especially the unique US outlaws should really be added.
Units
- Regulars replace Musketeers
- Sharpshooter replace Skirmisher
- Carbine Cavalry replaces Dragoons
- Gatling Gun replaces Falconet
- Unique US outlaws replace generic ones.
Enemies
They should use US Outlwas instead of generic ones.
They US enemies should of course use US units instead of generic ones.
The Asian Dynasties
Nothing as really been added to Asia in the Definitive Edition yet so no really need for any change in the Japanese and Indian campaign.
Act II: China
This campaign is historically very strange, you are supposed to play Ming China but everything looks like Qing China. At last the flag should be changed. Everything else would be a huge effort to change because most things in the Chinese civilisation are clearly Qing and not Ming.
Also the Aztec enemies are are not real AIs because back then you could own TAD without TWC so all units and buildings that were used are copies and not the original Aztec units.
Now with the Definitive Edition everyone has access to the Aztecs so there is no reason not to use the real Aztecs in this campaign.