I agree. I enjoyed Empire: Total War for two weeks after buying it, but now every campaign is the same. Race for the trade spots, plan what to build in each town, search for the same technologies, bribe nations into trading with you, fight off the suicidal one-province powers... I never even got past 1730 because I was already bored by then.

Come to think of it, Dawn of War II is pretty boring once you finish it too.

Someone mentioned Master of Orion; I never played it, only the second game, but I loved it and still play it from times to times. The diplomacy system was particularly good: you could ask people to stop wars, for example.