I think everyone (who plays such) has their own favourite Total War -game, it is still quite unfair to compare each others because, they all have their bad sides... even the fabled Medieval 2 or original Rome. I have to say, that original Rome was my personal favourite for a long time... because I was so damn good in it. I also hated Medieval 2, because its diplomacy made no sense (to me) and I got my bottom rammed every time I tried it. So... Shogun 2?
Total War: Shogun 2 is strategy game, mixing turn-based strategy, economy and army movements in campaign map, and real-time strategy in battles.
In campaign map you control and move your troops around the map, improve cities with new buildings or upgrading old ones and of course making diplomatic decisions for or against your enemies. In my oppinion, the campaign map is where you actually play
the game and you can, if you want to, skip all battles by using "autofight" option. Focussing only in the campaign map and its varieties will take, on its own, a great deal of time and demands that you actually think what you want to do and how and by what expenses. Luckily, the game has inbuild wiki/guide that helps in most of your question.
In battles you control your armies of sometimes thousands of troops and, hopefully, win. Game has fair amount of different troop types that support each others. Your job is to forge an army that conquers any foe and
you feel good to battle with.
*If you've ever played any Total War, you know how this works. And yes, that is a bad thing. Even if they have come a long way in 11 years from Shogun to Shogun 2, it is still Total War.
*The Shogun 2's diplomacy, however, is quite frustrating and a mod to fix it is highly recommended. You can make vassal states, you can forge strong relations by marriage and all other sort of stuff, however, when you conquer Kyoto, everyone starts to hate you. Everyone. Even that family, who has traded three daughters for your leader's sons and vice versa. When the "Realm Divide" triggers, all other factions declare war on you and if not well prepared... you will get your ♥♥♥♥ rammed.
*I'm not really sure, because some reviews say that this game has absolutely too hard difficulties. I on the other hand have had no trouble at all with the game and would like to note, that it is maybe a bit too easy in at least normal difficulty. Especially in battles if you allow yourself to pause the game, it becomes really easy and to massacre the enemy army of thousand spears stronger than yours, is not a big deal at all.
*Special clans as DLC? Special units as DLC?
*Moving your units in battle is fluent (as it should) and makes the RTS part of the game quite enjoyable.
*Big map, many routes, many enemies, many friends. The campaign part is good, way better than in any other Total War, which makes the game interesting even without a single battle. To keep up your economy up and running requires some attention, which is good, things won't happen on itself
*Varying generals who can be specialised into roles you want them to do on battlefield
*Steam Workshop. Because... if something is bothering you, you can get rid of it. Enabling mods and modding community is always a good thing
*Graphics and sounds are amazing (excluding the English in Japanese accent), music is good
In overall, the game is by far the best Total War so far, I don't own, but I've seen and tested the Rome2 and I can say that this rivals it totally. Comparing Shogun 2 to some old nostalgic games like Shogun, Rome, Medieval, Medieval 2 or more "recent" Empire or Napoleon is unneccessary. Shogun 2 gives you the feeling of Sengoku Jidai and the chaos and rivalry in late feudal Japan. If you enjoy more, lets say, story of Medieval Europe or some other setting, I'm sure tyou'll enjoy those games too, or more. But in gameplay and looks this game is teh best.
Me being one who preordered this back in 2011, I can say that I have not been disappointed and that that 30€ is not too much for this game.