Ahh, Civ V. Tried the demo on a weekend when I was feeling really rough and ill and picked up a far worse malaise of Civ addiction >.< Aside from dalliances with Age of Wonders, I'd never really been won over by turn-based strategy games. Civ V opened my eyes. I have since played Civ IV and although I enjoyed some aspects, I really didn't enjoy the combat system and everything felt a lot more complicated. But the diplomacy system was so much more expansive! It does seem a little too much was lost between each game. Good news on that front, anyway. A Civ V expansion is coming out in a couple of weeks that will add-in religions, better diplomacy and espionage once more. Should be good :-)
