To be honest, I don't really think you're missing that much. Having played a fair few hours of R2TW, I'm a bit disappointed. There are some fairly central mechanics which are missing from the campaign.
The whole thing looks like it's been slimmed down rather too much. The UI is kinda weird and doesn't really fit that well. The AI, both campaign and battle, tends towards being stupid. It's riddled with bugs. The multiplayer is a massive step back from Shogun 2...
While I'm being patient with regards to the bug fixes and optimisation, I'm not that convinced by a lot of the choices made by the devs in terms of the actual features. I doubt it will ever be as good a game as Shogun 2.