I've heard that Starcraft is taken deadly seriously in South Korea, to the point that it is an actual job and westerners move there to play it professionally complete with groupies
But yes, if you like Medieval, definately get the later Total Wars. Empire is my favourite, if only because that period of history is one of my favourites. It is markedly different from Medieval though; it might be worth just skipping ahead to Shogun II, because trust me, that game is nigh on perfect. It's a bloody masterpiece, and definately worth getting!
Hearts of Iron is the World War Two one with tanks and shit yeah, but you can be literally any country in the world. It is a game of strategy rather than the tactical level battles of Total War, and is really in depth. It's bloody scary at first, but once you get your head round it the depth of the game is amazing.