Like most people here, I have been an avid Civ player since Civ I, and I have to say Civ V is such an abomination compared to cIV BtS expansions, not to mention the worst of the series by far.
I believe I can speak for the majority of the Civ players here regarding features that absolutely must be brought back to Civ V, hopefully in future patches or expansions. These features are so essential to the whole Civ experience that I am not sure why Firaxis removed them in this generation.
1. We want our stack back: 1UPT makes moving units around so tedious and it's hard to get into formations in battle.
2. We want the old strategic resource system back: who came up with the idea that one iron mine can only generate one swordman? If I have an iron mine, I should be able to put it to use and build as many iron units as I want.
3. We want our slider back: the ability to shift the macro focus of your empire to either wealth/science/happiness is more dynamic than the current system.
4. We want local happiness back: CiV's global happiness system makes the game MUCH shallower, it's like playing a game for 10-year-olds.
5. No more purchasing units/buildings plz: it makes no sense to buy a building and it's suddenly there the next turn. Firaxis please remove this feature. Realistically, gold should haste the production process, but not producing things out of thin air.
6. We want religion back: religion is what makes cIV a much deeper game than all others in the series, including ciV. Why did they remove religion?
7. Bring back the graphics of cIV: as many players have noted since the game's release, ciV's graphics is absolutely terrible. Rivers and trading posts are just plain ugly. It's just about on par with Civ III if you ask me.
8. We want the old map grid back: sure, hexes are interesting at first glance and seems to make the game look complicated (reminds me of a boardgame), but after several games they begin to get on our nerves.
Firaxis, please pay more attention to what we the core Civ players really want. Until these problems have been fixed, I'll stick to my cIV.