First Impressions?

[Madae]

My biggest first impression is that a lot of the borders of the provinces changed. On the main four islands that was there previously in Shogun 2 and RoTS, I only noticed 2 provinces that are new. However, the borders of just about every province has moved.

The map does seem slightly larger, not just in land mass, but more as if it is "zoomed in" more. There are several new, one province islands though, along with a Kyushu-esque (without a land route to the mainland) island on the other side of the map near the Date starting point.

I didn't have time to actually play the game and mostly just looked at the tech trees and stats. Correct me if I'm wrong, but the highest tier buildings seem terrible this time around. I think the last gold mine upgrade, for example, is 10000 for a measly 300 additional wealth.

I'm going off memory here, but I believe the primary "money-making" upgrade was 1700 -> 2100 or so. Still, you gotta look at it from the long term. Without a gold mine, a province really doesn't make crap to begin with. I had a town with a gold mine making 11,000+ a turn by itself, compared to the 1800 my fully developed capitol was making. There are also several different bonuses that lower the cost of constructing buildings.

I don't agree that "all high-tier buildings" are terrible. Gatlings come from the highest tier artilerry range, Imperial/Shogunate Guard troops from the highest tier infatry buildings, many craft buildings have two routes to develop (better single province, or bonuses faction-wide), etc etc. If you want to upgrade a town completely, you'll probably need a max level police station to keep public order up vs. modernisation.

I started a game with Saga but am wondering about the unique units other factions have. Are there any limits to units like Tosa Riflemen and the Red/White/Black Hat infantry and so on?

There are unique units for each faction, but probably not the ones you're looking for. Tosa did have one - I remember seeing them running around with some - but I was playing Satsuma, and only noticed that I had some "bear-head" infantry that were not quite as good as the second-best (compared to Imperial Guard) Imperial Infantry.