If you're willing to put up with not-terribly-formed opinions and observations, here's my take so far:
  1. Graphics are slightly improved. No surprises there.
  2. Battle AI is slightly improved. Formations are held, arty is used, flanking is at least a possibility, and they daimyo isn't suicidal.
  3. Campaign AI is improved. For example, in the ETW build, if I hold a single well-stocked province next to hostile AI, all it can do is attack my well-garrisoned, well-fortified capitol. Now the AI will make end-runs toward those lightly-garrisoned provinces behind your big army. Makes life much more interesting. Amphibious assaults are to be expected if you don't protect your coastline.
  4. Diplomacy is improved in most aspects, although getting a peace treaty from someone whom you are destroying is as silly as in ETW (see Knight, Black).
  5. Between two and three options are now available when you conquer a province: (1) Occupy, (2) Loot, and most interestingly, (3) Liberate. Option 3 is not always available, but when it is, you create a new nation that (a) is your protectorate and (b) supplies you with some conscripts (1-3 units). Very useful for creating buffers with aggressive Black Knight neighbors.

That's all I can think of right now. Gotta get to work, too. Basically, NTW feels like a very polished, high-end mod for ETW, which isn't such a bad thing.