Well I don't think we can completely ignore MOO3... Without that disaster I would have never found GalCiv or Europa Universalis.
But yes, MOO2 was amazing I played that game from the moment it came out till around 2001. By far and away the best inveestment in terms of entertainment per dollar I ever made. As for memories of that game, probably the strongest memory, is being completely blown away by the size of the game... 60 Mb! At the time I only had a 100 Mb hard drive, I had to scrap every non-esential program out of my computer just to get the thing to work.
Additionally, this is the only game I enjoyed enough to play online, I'm strictly an off-line game player. However, MOO2 was the first, and so far, only time I've ever joined a gaming league, some Kali MOO2 league. I remember holding up everyone's game for thirty mins so I could download a 3 Mb patch to play online on some old dial up modem.
Great game, great memories