I played the demo, 100 turns never went so quickly.
I am extremely impressed so far. Everything seems so sleek and streamlined. Many aspects of Civ IV were confusing, but Civ V clearly explains the game mechanics and makes micromanaging more or less non existent. Compare the city screen in Civ IV to Civ V. Civ IV had a ton of stuff a lot of people never even touched, but Civ V's city screen is very basic yet gives you everything you need to know and do. I also love how they made money useful. A lot of stuff is too expensive early on, but I could easily expand the borders the way I wanted it. For example, I had two cities and wanted to connect their borders. Instead of waiting for the cities to randomly grow, hoping it would grow close enough to connect, I just bought the tiles between them and connected them in one turn instantly.
Combat is also really cool. I love how the stack of death no longer applies. You have to be strategic about where your units are and what you attack. I also like how it doesn't just compare numbers anymore, but instead gives you a text prediction like "Decisive Victory" or "Costly Attack." I also like the cities now can't be zerged early on. For example, I was attacking a city state, and fought a unit on the space behind a city, with my guys next to the city. I attack and we do equal damage. Then all of the sudden, the city hits me with boulders or something and kills my unit. Things like that will make me a lot more weary about attacking people for no reason. Although I only attacked them because another city state promised me goodies if I did.
I really thought City States would be an afterthought, but they are a huge part of the game now. Like I mentioned above, I met two city states (Budapest and Kuala Lumpur). Kuala Lumpur wanted me to take out Budapest, which I assumed would be easy, so I agreed. But when I attacked Budapest, Germany was all up in my face saying that they were friends. WTF, I had no idea. City States aren't just targets to take over, they are indeed a vital part of diplomacy.
Wow, I typed a lot for just 100 turns in a demo when I really wasn't taking anything seriously. I can tell this game is definitely going to be an experience and it takes pretty much every bad thing about Civ IV and eliminates them while adding in a lot of cool new ideas. I'm low on cash now, but I'm definitely buying this game as soon as I can.
And on a side note, can barbarians just spring out of nowhere? There was this small peninsula next to my city that I explored, and nothing was there so I moved out. Then several turns later, some barbarians from that direction started to edge closer to my city. They had to have just appeared out of thin air. I guess they could have been in a boat and come over, but I don't even know if barbarians can do that.