Shogun 2 is the best Total War game out of them all.
Gameplay
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There's much more depth added to game-play. One big notable change is the RPG elements introduced where you can select traits and abilities for your generals and agents. Unlike other Total War games, your generals and agents will now feel more precious because you manually chose what type of abilities they should have.
The game-play builds upon an improvement of Napoleon : Total War. There are some things you would notice such as the User Interface style which Napoleon had. For example, the loading screen to a battle will display a map and the name of the generals of each side.
Shogun 2 is the hardest Total War game to play to date because everything is precious. Back in Medieval 2, you could easily dispose units ; bowmen would have unlimited ammo and same goes for siege equipment.
Like in Napoleon, your ranged units will run out of ammo, which means you have to strategically plan how to use them. Same goes for siege weapons as they are very effective when attacking but can run out of ammo 5 minutes into the game.
Visuals
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The graphics are the most stunning for a TBS/RTS game to date. The campaign map has been beautified and you can rotate your camera on the campaign map.
For each season, there is a certain mood to it, which adds more immersion. Also, the season type depends on how a battle can result. If your men march in enemy territory during winter, your army will start to wear down aka attrition.
Shogun 2 forces the player to become very strategic and stops any attempt for them to play aimlessly. Those new to the Total War series may find it difficult to get into Shogun 2 but I don't blame them because it felt like this game was made for Total War veterans anyway.