Civilization 4 is garbage without Beyond the Sword (which itself looks like garbage compared to any number of mods).
You can't go wrong getting Civilization 4+BTS though. You'll probably squeeze a few dozen hours of game with it before resorting to mods.
And don't listen to the stuff about corporations. They were pretty terrible and useless. The only time I bothered with them was when I played with Realistic Corporations in RAND. Those corporations were actually fun, not mindless executive micromanagement.
Espionage, again, terrible. Too much microing for not a lot of return. I'm glad it was dropped in Civ5.
Religions were pretty pointless to outside of manipulating the AIs. For some reason, religions often turned into power blocs in their own right when realistically, you'd be hard pressed to say Catholic Spain and Protestant England were on the same side of anything. In game terms, they're both Christian and since all Christians are the same, these guys are best friends. It's really eregious when you see a scenario with a Islamic Arabia and Persia and see that they're friends because they both have the same religion.
Again, A New Dawn has Ruthless AI which is probably the most rewarding and interesting AI to play against.
UN Resolutions were pretty stupid too. Why are are these resolutions binding? For some reason, the UN in Civilization has the authority to check every nation on the planet for nuclear weapons and force them not to build anymore. You can't leave the UN either and defying a resolution makes your people unhappy. I hated the Diplomacy victory because it was pointless. It got better in Civ5 but then again, its still an economic victory unless you're playing with City State Diplomacy.
Wonder movies? Meh. You'll watch each one once, maybe twice and then skipping over them. That's why they didn't put the time to making any. Now, the victory movies are different. I loved those (except the diplomatic victory which, like the victory itself, is pretty hollow).
Diplomacy was easy to manipulate in Civ4 (again, without Ruthless AI) but its far better than Civ5's.
Civics....were STUPID. Oh my God, I don't know who came up with them but they certainly don't make any sense. Running a monarchy makes people happy when there's a huge military garrison in the city? I didn't know that. I'm sure Rome, which had a legion marched into it every other year, was certainly not happy about that. Who would've known that the Caste System was the ultimate system of social mobility? The whole corporations thing is ignored once you get the best civic, State Property.
Oh, and Environmentalism actually contributes more to Global Warming then it stops it. Recycling Centers are especially bad when it comes to fighting global warming.
In short, espionage, religion, and corporations are pathetic without certain mods. Revolutions is a big one. RAND a big one.