Difficult to pick only one, heh. For strategic games we still love the Civilization games, though we never played the newer ones. A bit too big for our perfectionist minds, we'd never finish any game with all the new options haha!
Also Emperor, Rise of the Middle Kingdom deserves a mention as it precisely fits our intersts.
We also still love to play Ultima Online, the options in that game seem limitless and we feel always short on time with too much we want to do or achieve.
And of course we also have to mention the Final Fantasy series, the storylines, the music, the characters (most of them), what's not to love?
:D