Answering the Critics

[Unwise]

I'll take a shot at this. Have your buddies try and look past the "Civ IV City = Dom 3 City" thing and try to have them see what aspects of the game are actually equivalent.

Improving Something
Really, the Dom3 equivalent to a Civ4 city is a commander. You buy it, you assign units to it and you provide it with upgrades. In Civ4, an upgrade would be an aquaduct. In Dom3 the improvement would be a Sword of Sharpness. In each case, the improvement is based on resources and also on where you are in the resource tree.

Economics
As others have pointed out, gold and resources are not the Dom3 economy by any stretch. You have to add in the seven gem types, blood slaves and dominion effects. This is pretty much on par with Civ4's gold, resources, luxury sites and special resources. It would be tough to call either model more or less complex than the other one... though I think that the dominion effects would tend to tip the balance towards Dom3.

Research & Technology
The Civ4 tech tree is roughly equivalent to the Dom3 spell research grid. How you research is a bit more complex in Dom3, but not too much more. In Civ4 you get to build new units and buy new structures after gaining a new tech while in Dom3 you summon new units, cast new spells, and build new items for use with your commanders. Pretty much dead even.

Globals
In Civ4 the globals are "cast" by building wonders that you gain through research and pay for using gold and resources. In Dom3 you cast globals as spells that you gain through research and pay for using gems and blood slaves. Not much difference there. Dom3 adds a slight layer of complexity to the formula in that just completing the research does not guarantee that you have the proper commander/mage necessary to cast the spell.

Nations
Civ4 makes nations unique by giving them a single unique combat unit and provides the nation one or more advantages ("industrious", "militaristic", etc.). In Dom3, all races are given "unique" units for all purchasable units and provides some nations with special advantage/disadvantages (blood sacrifice, scrying, etc.). Tough to make the case that Civ4 is anywhere near Dom3's level of complexity here. Comparing the differences between England and Germany is laughable if you compare the differences between, say, Ulm and Mictlan.

Combat
Another area where the differences are pretty severe. First, comparing a IGO-UGO system to a WeGO system is apples-to-oranges... you'll never come up with a "winner" because they aren't playing in the same ballpark.

That said, it's hard to look at Dominions' dozen or so combat statistics (including poison, fatigue, morale, strength, precision, and others) combined with the tactical battlefield (range, temperature, positioning, castle walls, etc.) and compare it with Civ's fairly straightforward combat system.