Your reply doesnt really answer my question. Did they remove things like micromanaging things that served no real purpose? Did they remove crucial elements? And your comment about being able to beat civ 5 on immortal after 45 minutes is absurd. I have played 44 hours and still can not beat immortal. The only civ I've played is civ rev and civ 5 seems like a giant step forward. I have my hands full every turn, I don't know how much more they could add to make me micromanage. This game has more micromanaging for me than simcity 4 had.
You're question is very difficult to answer, if you haven't played Civ 4. It's like asking someone to explain the difference between the Mona Lisa and Michelangelo's David. They'd have to write an several pages of essay. To be more appropriate, it's like asking "I've done science in school, how will a physics degree at university be different?"
You really should just get Beyond the Sword, because it will be an year or two before Civ V gets to that level of depth.
And I think my post did sum it up. Basically, there's a lot more mechanics involved in the game - cultures, religion, espionage, health, local happiness, corporations, foreign trade, economics. Each was deep and interconnected to the other mechanics - as with any game, every mechanic that is balanced and well intertwined with the rest of the game increases the complexity exponentially, which is what made it so interesting and long lasting. This also meant you can't change one aspect of your empire without everything else being affected in a chain reaction. You don't have the kind of simplicity of Civ 5 where science is a factor of population count, so your empire could be at -20 happiness but still producing as much science and gold as normal.
In Civ 5 there are fewer variables to balance and the game doesn't punish you too much if one of them goes astray. Civ 4 is not that forgiving and you need to keep a lot of variables in your head. Having to balance all these mechanics made for several years of deep gameplay, because it took a long time to figure out foolproof strategies, even though the AI was not the sharpest knife in the drawer.
I didn't say you can win Civ 5 in 45 minutes - that still takes 400+ turns (only because everything happens so slowly in it). I meant that in about an hour after installing it, you can basically "figure out" the perfect strategy to win, even at the hardest level. After that, there's nothing interesting in the game any more. I just got bored after beating it on Immortal. I know others are beating it on Deity, but the game is just too boring to make me try. In Civ 4 there were so many mechanics, so much going on, it took a long long time to be able to understand it to this level. In fact, I don't think even now I understand it that deeply.