This is in response to the numerous polls and suggestions that Civ V is "dumbed down" or less complex than Civ IV. I do not mean to suggest that Civ V is perfect in its current state (it needs obvious bug fixes and ai improvements, probably a little building rebalancing also). What I do suggest, is that Civ V is certainly more complex in its basic mechanics than Civ IV. To wit:
Building maintenance- Civ IV had no building maintenance costs. This made the decision of what buildings to build, and where to build them far simpler, a step backwards in complexity from even Civ I and II. In IV you could spam every building everywhere in your empire, without regards to min/maxing or whether it would be worth it or not. Try that in Civ V, you will bankrupt your empire.
Now it is even simpler than in Civ IV - you don't need to built anything at all. In Civ IV, you would suffer being underdeveloped, here no problem - better to train another archer or horsemen

Beside, every captured city, you can set as a puppet - so they will create what they want, when they want. That is a great simplification.
Combat- Stack combat was a gross oversimplification. Build some melee or gunpowder units, a bunch of seige, group together and click go-to button next to enemy capital. Not exactly rocket science. Now, in Civ V, one unit per tile is infinitely more complex. So complex, in fact, that the ai has not mastered it (one of the actually legitimate criticisms of Civ V). However, I appreciate the more rewarding and complex new mechanic, and look forward to vastly more exciting and complex multiplayer action, and single player games after ai improvements.
Yes and no. In Civ IV, it was not easy to capture a city - you usually needed to level down its defences first. Beside, every city taken usually mean some casualties. Now you have no casualties and with few units you can conquer the world.
The only change made is that "monster stacks" were replaced by "monster units" - so if fact it simplified everything even more. Just make 2 Horsemen and go and take half of the world - even playing against human player, as it seems horses incredibly well climb up the ladders when besieging cities.
Government- In Civilization 4, your choice of civics had zero long term repercussions. You could easily change Civics after a short period of anarchy, even that easily mitigated by golden ages or religious trait. While admittedly slightly less simple than the likes of Civ 2 (where you could run democracy, then pop into monarchy for a couple turns to declare and fight a war, then pop back into democracy) even Civ IV’s civics system is very simplistic. By contrast, in Civ V, you have to consider several things when adopting a social policy- the short term versus long term benefits not only of the current policy choice, but of all other policies farther down the tree. You really have to plan ahead with a grand strategy, making social policies in Civ V much more complex for the player than its predecessors.
Before, you were forced to think, which solution is best for you in a given time - now you don't need to thing - every your choice is good and you don't need to worry you chose something incorrectly, soon you will be able to choose the bonus you need.
Expansion- Prior civ games had no effective check on expansion. Founding an additional city was nearly always advisable, bigger was always better. In Civ V there is a very real cost to reckless expansionism. There are benefits too, and therin lies the essence of complexity. A larger empire will generate more hammers and gold, but it will be difficult to keep happy. Founding a city to gain an additional resource may help with happiness or military power, but detract from your ability to accumulate social policies. There are all kinds of tradeoffs, and the optimal strategy may very depending on your situation and what victory condition you are aiming at.
Not likely, because of maintenance costs such as distance to palace and number of cities. Now you can found a city of a different continent and it will act exactly the same as 3 hexes from capital. And happiness? Before it made a difference -because it damaged city production. How it just makes people to have less sex

(shouldn't be opposite?)
To be honest I stopped paying attention to happiness - in fact it doesn't change anything. Even this -33% fight modifier can easily be levelled by super upgraded unit or just more units.
Happiness- Civ IV had the easiest and most simplistic happiness system in the series. Not only did your cities only have localized happiness, but they didn't even experience revolt or civil disorder, merely an unproductive citizen. You could effectively ignore all of those angry faces in Civ 4, until you got around to dealing with them. With Civ V global happiness, you ignore happiness at your peril. Reduced empire wide growth, lack of golden age accumulation, loss of rationalism science bonus, penalty to combat, etc. (I am aware of the existence "ignore happiness" strats, but these are mainly for specialized late game situations. Further, I believe they are something akin to an exploit which will be fixed by increasing the "very unhappy" penalty in future patches).
As above. I played a whole game with average happiness -15 and that didn't change anything for me. I was still able to conquer city after city and didn't bother about such details. In Civ IV, you had to look in every city, what are the reasons behind unhappiness as there could be different. Now, you don't need to bother - if you have enough puppet cities, you can be sure, some of them will finally build some colosseums, to solve the problem on the other side of the continent.
This is a simple approach
