Converting the world to your religion is fun. In my Earth game, I am currently a Jewish Pacifist nation; India, Egypt, and Persia all belong to Judaism as well. I have an Alliance pact with Persia (they're my other favourite civ). Right now I am working on converting all of China to the religion, Rome and Greece used to be Jewish as well, but we fought two massive wars and now the Greek Civilization exists in Northern Asia and the Roman Civilization in Africa and the Americas. The Mongols were never friendly with me. The Romans, Mongols, and Greeks are all Hindu, a religion which originated in Persia, but Persia is a Jewish state.
The last, the Japanese, I have not had much contact with them, they hate me, and they are Buddhist, the religion is completely confined to their civilization which spans over Japan, Oceana, North America, and a few mainland cities. A lot of nations have their borders closed off to me, China is Hindu as well, they have open borders to me, but will not convert to Judaism because I co-operate to closely with their biggest rivals (the Persians). About all of Eurasia is colonized, Oceana is almost colonized completely by Japan, and the Americas have a few colonies of various nations.
Currently I am about to abandon the religious path, I have chosen to go the Nuclear path and bring on the Neon judgement against all of those who will not adopt my faith =)
I am going to say right now that this is easily game of the year in my book. FF12 and Twilight Princess aren't out until next year, so I don't anticipate any serious competition between now and March. There were some very strong titles that came out this year, but nothing else is Civ 4.
Oh yeah, a few more things, if you remember the fungi, or whatever, in Alpha Centauri, trees work similarly in this game; they grow back over time around places where a lot of trees exist, and they harbour wild animals (similar to how the fungus housed those mind worms in AC). I wonder why this wasn't in Civ 3? It is a great addition to the game I find.
This game actually does have a very Fire EMblem like strategy system, it is a good thing Sid was paying attention: you can upgrade units to fight more effectively against other types of units (IE. +25% against gunpowder units, +50% against melee units). There are many different categories of units as well; so it isn't like Civ 3 or earlier games where the key to success is building 30 Crusaders or 30 Swordsmen; because a smaller army of axemen would wipe out the swordsmen.
Siege is a factor in the game now (they had an early version of it in Alpha centauri) so when invading a nation, it is essential to bring along your catapults or cannons, otherwise there will be difficulties taking the city. Siege equipment lowers the natural defenses of places, and unlike civ 3, they also exist as a usable unit as they had in earlier games, rather than one to be captured (only workers seem to be capturable in the default game). Siege equipment is also good in cities as it can cause some minor colatoral damage to armies, which can turn the tide of the battle. Speaking of armies, you can finally group together HUGE armies and fight battles againstother huge armies, it is no longer a game about 50 smaller units, rather combining those 50 smaller units into one gigantic unit. Of course, the individual units can be separated at any time, but usually you would only do that if you need some units to garrison a place you captured.
Anyways, this game is fucking addictive, since I have got it I would estimate 15+ hours in two different games, my German game on the Earth map is almost complete though, my Persian game is in its beginning phases. Speaking of which. What I have observed with the flow of the game, the archaic age lasts a lot longer than it did in any of the previous civ games, I spent a couple of hours on it. The next age is the Classical era, which is essentially the Roman/Greco era, that also took about two hours. Medieval, Renaisance, Industrial, and now the atomic age; more eras, and they are much more even. It is not like Civilization 1, 2 and 3 where 90% of the game is in the Industrial and post industrial eras; it is split up fairly evenly. I am not sure yet, but I think there is an Information age coming up as well.
-Insert Inspiring Quote-