The custom palace for fun.
Global view
Atack and defense stats where you can build offensive melee for attacking and defensive spearman for defending, especially citys.
Random events
Vassals and colonials
local map trade, tech trade.
The tech map being more free and complex to choose from. Now its pretty restrictive and shallow. You could really push for certain wonders or units faster by going with a certain branch. I would like in a future civ, the tech-map to be wider with more possibilities before you enter a new age.
Agreed with most of these, especially the palace and attack/defence stats - also the tech tree structure, but it was only really Civ IV that had a more complex one. Civ V has about the right number of techs, but I'm not a fan of the tech structure and it has produced a few balance issues, such as the perceived weakness of the 'iron working path' (a major conceptual problem given how fundamental metalworking techs were in reality).
The remainder would, I think, warrant reworking before being brought back. Perhaps a Great Merchant ability could be to establish a colony, which would act like a Freitoria for 'neutral' resources with its own small territorial radius? The Conquistador could replace its settlement ability with a colony.
Vassals weren't well-handled in Civ IV, and in fairness aren't well-handled in most games of this type; vassalage is almost always by military domination, when it will only be accepted by a loser you could conquer anyway, and as all Civ games suffer from rather static balance of power (i.e. dominant civs tend to remain dominant, weak civs to remain weak), vassalage is basically irreversible within the system. However, it did help allow Civ IV AIs to play domination more capably than Civ V ones.
Tech trade was abusable in the past (selling the same tech to everyone for multiple techs in exchange); I'd rather see a modification to the research agreement system, whereby two civs agree to jointly research a specific tech that neither possesses, as long as at least one of them has the ability to do so.
Random events were always part of Civ, but IV killed them with balance problems - bringing them back in much less drastic form, and being less common, would be welcome.
Other things I miss:
- Barbarian huts. The risk of triggering barbarian spawns when exploring tribal villages (I also miss them actually being tribal villages, which among other things makes a lot more sense than stone ruins in 4000 BC) added an element of trepidation to exploration which was lost when Civ IV removed the system.
- Resources spawning when land is modified. Coal that can appear when you build a mine, or grassland resources when you clear a forest, etc.
- Civil wars and the spawning of new civs when they occur (Civs I & II, can't recall if in III).
Problem with Civ 5.. there's is barely any penalties. everything you have is a bonus.
That's more of a systematic design issue than something specific missed from previous games, and the series has been moving in that direction at least since Civ IV (free bonuses from researching techs, only goodies from tribal huts with no risk of barbarian spawns, health bonuses for settling in desirable terrain/connecting desirable resources, removal of corruption, free bonuses just for having religion, and for each religion in the city, free accumulation of 'espionage points' rather than having to spend hard-earned gold, free diplo bonuses for open borders and trade with no downside etc. etc.). Civ IV had opportunity costs from civic selection and - like previous games - from the slider that are reduced in Civ V, but it offered few penalties and one of the few that it did - pollution - has already been mentioned.
You'd almost never see it above king. Your influence has to be pretty high, they also need to be extremely unhappy. I think it does need to be neg 20. Been a long time since I flipped a city. I don't like what cities it picks either. I think it goes by the one producing the most unhappiness. That means it's either a big high pop city or one with very few or no local happiness buildings. Last time I got one to flip it was the Zulu's second city. He had built a couple wonders in it including the Louvre. It actually felt like cheating getting that city.
I've only played on Emperor and Immortal post-BNW and I've seen it a few times, though was only the beneficiary once. Frankly I find it the weakest feature of BNW; it seems an illogical "because it was in Civ IV" add-on but with none of the utility it had there. Moreover I feel it misses the point: in Civ IV you weren't interested in city-flipping so much as tile-flipping to get useful territory, and you had direct control over where to focus your efforts in order to get the most from your cultural output. It also gave an importance to local (i.e. city-level) culture that's missing in Civ V. In Civ V, you have no direct say in which city will flip (or even which civ it will flip from, which you can but influence by maximising tourism), and you're racing against other civs with your ideology to flip it to you instead of to one of them.