It's been 10 years since I played Civilization, and never got my copy of Colonization to run back in the day, but this has all the turn-based, resource-building goodness I remember. It's a beta that the authors admit isn't quite up to where the original was yet, but it still rocks.
I'm still re-learning how to allocate resources, pick out good spots for a city, what buildings absolutely have to be built first, etc., but even without having a clue about any of that, it sucked me in.
Must be careful to actually get some work done rather than sit back and play this for days on end...
Feudalism: Serf & Turf