Summary: The only complain I can find with Shogun 2 is the lack of units. Of course you can download mods that add a bunch of different units, the Saints and Heroes unit Pack gives you legendary warriors of Japan. Their stats are much higher than their regular counterparts but they are not too powerful where they can dominate the entire battle. Used well, they can change the outcome of small fights within the larger battle.
Summary: This game is hard to work out. There are no clear guides on how to play and even the online help sites don't really make it clear. It may just be that this game has a very complex game engine but after trying it 4-5 times now I'm just ending up frustrated and dead.
Summary: After beating Shogun 2, I was left wanting more so I bought both the Rise and Fall of the Samurai expansion packs. Rise of the Samurai is practically the same thing as Shogun 2 except three major differences: units/forts/technology are more primitive, you play as a part of a larger faction, and the agents' roles have been reworked.
Summary: So, you want a new Total War game? Sure, you could spend $60 on Rome 2, but it's full of bugs, performance issues (even after 4 patches) and missing a lot of features that made previous TW games fun. For half that price, you can get one the best entries in the series, plus its two expansion packs. For $30, Shogun 2 Gold is a great value.
Summary: The game is just too complex and for those who are not die hard Total War fans will have problems going through a long campaign mode. The in-game battles are fun and at times difficult but the challenging type of difficult. The economic part of the game is just downright frustrating and for me was the thing that killed the whole game for me. As a fan of Japanese history I was excited to play this game but I never was able to feel comfortable or excited about any clan.