Like you say, there are many obvious things like religions, espionage, corporations, sliders and such things.
But that apart the game itself is much simplified. Its hard to say all the things. It's not only consistent things like the lots of info screens and graphics we miss (and we miss them a lot sniff). But also not tangible things like strategies around switching civics for some toruns to achieve something and then coming back. Or forcing the AI to switch so he can't do that or that.
Those are just 1 examples of many things in that style.
Yesterday I also read a good post explaining how something we don't even think about it has been made easier. And again, it's only an example, but after reading it I started thinking about many similar things where the same happens:
nother problem is stuff is so simplified it makes me cry. Lets take happiness buildings for example.
Civ4BtS: Monument gives happiness if you're charismatic. Temple gives happiness but you can build it only if you have religion. You can build more than one if you have more than 1 religion. Also temple can give you a bit of science / money / hammers under appropriate circumstances (University of Sankore, Minaret, AP). Then we have Marketplace which gives happiness only if you have some certain resources. Then there is theater and Colosseum, theater gives happiness if you have dye, Colosseum just gives +2, and both give happiness for culture %. But that's just buildings and I didn't even mention UBs. There were others ways to get happiness. Being charismatic, adjusting % slider, resources ofcourse, even whipping (i.e. reducing population) was a legit way to make unhappiness go away under certain circumstances. Religion but only one of all possible and only if you made it you state religion; unless you have Free Religion civic adopted in which case all religions give +1 happiness each. Do you see how many different interesting stuff we had? How many possible interactions? How many possible ways of playing?
Now what we have in Civ5? A short list of buildings which can only be built subsequently and all of them gives some amount of happiness in exchange for some amount of maintenance, every single building is basically a variation of the same, just maint increases.
This is just one small example. I didn't even think that hapiness buildings were less complex before reading this. And then I noticed there are lots of small areas which have been simplified like this: changed for a line of buildings, each one just costing 1 more maintentance. This little things you don't even notice, but adding all togeather you have lost a lot of complexity