The new update for civ 5 I wrote about a few days ago I think has gave some good new improvements. A very good graphics performance which makes sure you don’t need a very powerful graphics card.
I think the biggest thing that has improved in the update is a thing you might not have recognized but I have recognized that the AI was now much more mature. It acts more normal you now know if you do something bad to a leader you know that they are going to be unhappy with you. Also leaders now just don’t randomly declare on you when they have good relationships with you.