I've been strongly thinking about buying this game.
I absolutely loved Shogun 2 and its expansions, one of the best games I ever played but I really hated everything about Rome 2 (and didn't bother with its expansions).
Should I just bite the bullet? I know absolutely nothing about Warhammer.
Read the following questions, if the answer is yes to them you should get the game in my opinion.
1) Do you like fantasy?
While there are more traditional factions like empire and dwarfs most factions will play very differently from historical total wars. For example vampire counts have NO ranged units, not a single one, no archers and no artillery but they get some strong flying units and their units don't rout.
2) Do you mind lots and lots of DLC?
CA has said the warhammer game is a 10 year plan and they will be releasing 2 stand alone expansions, in between expansions you will get tons of DLC. For example the game has been out for 2 months and has 3 DLC- warriors of chaos (faction), blood and gore (new animations and add blood) and beastmen (faction+mini campaign).
3) Do you care about heavily managing your cities?
total warhammer kinda streamlined the provinces making the game more focused on your armies and on the battles (i really like this change)
4) would you mind that the siege battles would be with just 1 wall alongside the map instead of a full settlement?
This time CA completely changed the siege battles, for me they are much better because the AI works better and the walls are much bigger allowing the movement of troops easely, however you no longer defend the whole settlement, you just defend that wall.
Personally total warhammer and attila claim my favorite total war. What i like the most of warhammer is that each faction is very different in some ways playing with different factions feels like a new game to explore. Another example dwarfs have no cavalry but have very high morale and very high armour, makes for a very different experience in the battlefield since you will always be flanked because you have no cavalry.