3 out of 5, frankly the unfinished 1861 scenario was too sloppy. I also mark it down because the military part of the game is still be more like a crazy brawl combined with whack-a-mole than a front-based waging of military campaigns. Attrition in foreign territory seems excessively high. The AI also still declares all sorts of lunatic wars. The research system remains pretty bland, and offers no trade-offs (Magna Mundi for example is great for the trade-off approach it takes, instead of the linear progression approach). Research is also feels too isolated an affair - I didn't get the sense that you could catch up if you fell behind, because you have to do it step-by-step on the different tracks and there are lots of tracks. It would be nice if there was a kind of tech and invention spread among the countries, with a bonus to civilized countries. I'd also favour more of an an 1880s "rush" for colonisation, where when the first person gets a certain invention it unlocks the region for everyone. As luck would have it, I had a scramble between the UK and France, but noone else got a look in except the event driven creation of the Congo Free State which went to Belgium.
The diplomatic influence game and the relations still feel like two seperate systems, and influence still feels a tedious chore that relies on timing and micromanagement. It also still sometimes hard to understand why you can sometimes get allies and sometimes not; admittedly my game was with a badly off Sardinia-Piedmonte because I couldn't sphere Lucca and Parma and I had no opportunity to hit Austria until the 1870s, so I accept I wasn't exactly a catch. All the same I preferred the system in EU2 with the alliances handled as blocs which you joined, or Vicky 1 when the balance was somehow right (or at least, the random aggression was lower). The AI is evidently a bit confused, because e.g. France didn't conquer Algeria or Tunisia but did get in lots of fairly pointless wars with Spain and the UK... Yeah the aggression needs to be channelled somehow against more viable targets, or the costs of a failed war against a modern foe need to be higher. Tthere were lots of white peace conflicts which should never have started in the first place. Consequences for breaking the European balance of power need to be higher, consequences of defeat in a European war need to be higher, and the AI should treat such consequences with a relatively higher sense of caution. I understand that it's hard to get Prussia to kick off the wars of unification, but some cheap and cheerful cassus belli conditions given at appropriate times (i.e. when certain conditions are met) would go a long way here. We don't need determinism, but we could be creative about setting up a nice balance to the game which has a feel of both plausibility and flexibility.
For all that it's a good expansion, lots of features are enjoyable. I think I'll now be able to enjoy Vicky 2, especially if I give multiplayer a go. Oh, and for me at least, it's pretty stable! That's what ups it for me from a 2 to a 3.