I was disappointed in the game. It has many great features, and in many respects was an improvement on prior games. However, compared to Empire Total War and other TW titles, it has far less replayability and diversity.
There are only a handful of units, all the same for each clan. The bonuses for each clan is also, in my opinion, limited. Its more like merely choosing your starting location instead of a brand new faction. Compared to the wealth of countries and units in prior TW games, Shogun 2 is quite bland. I finished the campaign once, played a few multiplayer battles, and already feel like I've exhausted the game.