The game is all about leaders which is a new mechanic. There is a new wonder and four new guilds but other than that everything is Leaders, Leaders, Leaders. Read that in Jan brady's voice. You now have a leaders phase after you pic you wonder. In that phase you draft three leaders that will help you in the game. They are brought out at the beginning of each Age. Most are end of the game type things but some are used as soon as they hit the board. They work like any other card being active in all subsequent ages of the game.
We had a few hiccups in our game with this. It slowed it way down at first which was OK as we were chatting. Also there was a large amount of clarifying the leaders cards while looking at them. That was sort of weird as they function more or less the same as the main game. Also there is some weird thing where you can duplicate a card ( With Olympia B) that duplicates a Card (Courtesan Guild) and that just got confusing. Another odd thing was I got an extra promo with my expansion but no rules for it. I guess Stevie costs nothing to bring out during the leader phase but costs when you use him to build a wonder stage. We just didn't use him.
All in all everyone seemed to be positive on the expansion feeling it helped and added something to the game that was needed. It is also pretty similar to the game play so it will not re invent the wheel.
Still something I would like to see would be cards that allow you to screw with your friends a bit more. I would like a leader that lets me swap a -1 military failure for a +5 victory at the end of the game. Maybe an expansion that looks different enough that you can pull it in and out of the game when you want.