Now im soon done with my 4th session of Civ5. I guess i have come to some conclutions. Most things are improved to the better, except the combat system. It makes a new way of strategy, but more like a boardgame strategy not representing real combat on a global scale. Sometimes it turns out to be very ineffective with units blocking eachother and to take a city may take several turns longer just cause of that.
The ranged units is a very good improvement. That you actually weaken the unit with artillery, not just erase their fortification bonus. I guess the cooperation between land units, ranged units and planes is alot better. You need them all, alot more than in Civ 4.
Ive won conquering victory, diplomatical victory and now im trying cultural victory. Though no war no fun. I guess i usually will go for military victory in the future.
Golden age is also alot more relevant in this game. You may get unlimited golden ages i think, compared to 1 or maybe 2 ( i think ) in civ4. The city states, natural wonders, and the new sea-transport system and all of it is alot better than civ4 imo. And best of all, no religion