I haven't played 3, or 2 for that matter, but the original GC was an incredibly great game. The AI was insanely good, and I don't mean "just steamroll you good", it could actually think and plan not just militarily but economically. If it was losing a war to a superior force, it's smart enough to know to hit and run your trade routes so your economy collapses and you're forced to disband your massive navy, for instance. I don't know if they're still floating around the internet, but the designer of the AI system did some AARs that were actually very good where he not only plays the game, but explains how the AI is coming to the decisions it makes as he's playing it, and, spoiler alert, of the 5 he posted, he only won 2 games I think, the AI is that good.