First Question: Have you any familiarity with the Total War (TW) Series?
If no, first let me explain a bit about them
If yes skip the first bit...
The Total War series is a turn based strategy game with Real Time strategy in-game mechanic as well.
The way this is done, is by having an open world, where ones does all the moving about with armies and city planning, as well as diplomatic relationships and Etc. Further more any battle can be chosen to be played on the battle map, which is a real time style of game play, where you can move about your forces and command them, it allows for pausing the game and speeding up, should such be necessary. In the open world map, there are cities and town, all with multiple adjacent cities or towns that are considered a province (A concept which where introduced in Rome II), owning a province gives certain additional features, so in general those are neat to own.
The general idea of the games is to conquer territory, fulfilling objectives and building the cities up to an impressive standards. As such much of the game is in principle done in the turn based over world, you can even play an entire play-through, without ever actually doing any RT fighting.
The Game take many hours, especially if one desires to go for the Grand Victory condition, which of course means that it does become a longer session game.
It's in general a great strategy-game series and I recommend pretty much all of them. There is a lot of depth and great measures for strategizing over, Ex. which buildings will give the best results for the over world, and the tactical option for the RT parts is always very engaging.
NOW for the Warhammer 1, bit:
So far I feel like this is probably the game with the most endurance of the series. Every faction plays uniquely, even among similar(ish) races, such as Britonia and Empire, whom both have very different core mechanic attach to their campaign. The battles are fun and just as engaging as any other game, if not more, with all those cool creatures joining the fight

most of the spells seems to be useful too, they do not overwrite good tactics and you can win, even without fielding a mage, despite fighting an opponent with several (Take that for good or bad if you will).
It's really a descend polished game, even one of the more new comer friendly. Which Attila (the one prior to Warhammer) was certainly NOT
SO yeah, great game series and Warhammer is even one of the better of them