I used to play total war titles (not so much anymore at the moment) and I would sum it up like this: I play Paradox games for the gameplay and total war games for the atmosphere. For me, campaigns in a TW game have the main purpose to create dynamic battle scenarios. The battles themselves don't have a real strategical value, they can be tricky sometimes if you need to micro-manage your troops a lot (you can pause all the time but that in turn has a negative impact on the atmosphere), but in general beating the AI is trivial. The strength of TW is that it's like an interactive Hollywood movie which can create great looking and sounding battles. I'd actually go as far as to say that TW is badly designed as a game, but still it is worth to be played.
Medieval 2 is my favourite game of the series with Rome and Empire coming second and third respectively. I did enjoy Empire TW, but I still regard it as an unfinished game with strange design decisions, e.g. the way the map is designed has such a big negative impact on gameplay. Too huge provinces (France!), too many empty areas on the map (South America cut off, no Sub-Saharan Africa, and what really hurts is that Russia is cut off at the Urals, Central Asia is wasteland [wtf?] and East Asia doesn't exist). After Empire, I didn't really play any of the newer titles, instead playing Medieval with mods.
