As a player of the original Sins all those years ago, I'm liking what I see so far but have some suggestions and thoughts on how subfaction design should be handled and improved upon compared to Rebellion.
Subfactions all need a very clear and recognizable theme and personality. The Rebellion expansion for the first game did this very well for the TEC, all of the unique techs for TEC Loyalists and Rebels had a clear purpose and gave them their own personality and Sins 2 is doing well in this area too.
So far though, TR get 2 unique units/structures and far more unique techs compared to Loyalists which feels a little unfair to me, not necessarily balance wise but in flavour. For TL, I'd like to see them get minefields or a unique version of the Gauss turret. For more unique techs, I think it wouldn't be too imbalanced to give them more techs to improve unit toughness, planet health/regen, trade income etc. Maybe some existing techs for both could become TL exclusive like Pervasive Economy.
For the other factions, I felt that in the previous Rebellion expansion, Advent/Vasari subfaction personality/theme was not quite as well designed as for TEC. Some unique techs seemed bland especially for AL and others didn't seem to fit their subfaction's theme.
For AL, since they are supposed to be continuing their crusade, but in Rebellion their unique techs were more about strengthening culture spread which isn't that strong or interesting on its own. AL may again get a % chance to capture enemy frigates when they try to leave AL owned planets and a Titan that can instantly capture enemy planets. I'd like to see their unique techs expand upon the theme of stealing stuff from the enemy, but not necessarily just ships. They could get a means to steal a % of enemy trade income when they have capital ships near enemy trade ports or use their mind powers to cause insurgencies on enemy planets.
The AR had an interesting theme of religious reforming and of self-sacrifice and rebirth but some of their techs seemed a bit irrelevant and in Sins 2 I hope for greater consistency. Their techs to boost shield regen in culture and shield recharge seemed a bit too generic and their AM regen buff when bombing enemy planets didn't seem to fit them at all. In Sins 2, I'd instead like to see a focus on frigate resurrection and on the ability of dying frigates to boost nearby friendly ships. Wail of the Sacrificed was a cool concept but wierdly implemented and strangely aggressive for a faction who wants to change direction instead of pursuing revenge. If Wail makes a return in Sins 2, I'd like to see it become a defensive ability for the deliverance engine that causes AR planetary population to self-sacrifice to damage invading enemy fleets.
As for the Vasari, the VL were supposed to be packing up and leaving in Rebellion. If stripping planets down to dead asteroids returns, it should be a major investment for resources as well as time, it could be an expensive ability for Starbases.
The VL had a very unique mobility-based theme but this undermined slightly by the VR also buffing mobility by gaining phase-jumping Starbases which I would prefer not to see return. VR were supposed to have a theme of cooperation and warning the other races but some of their unique techs buffed their damage output which was too strong and too aggressive and out of place for them. VR unique techs I feel should stick to the areas of trade, diplomacy, black market etc. and leave military and mobility themed upgrades to the VL.
