I'm probably a bigger fan of the Cities expansion over Leaders. In all honestly this expansion does add to the overall theme of the game, especially as it relates to players individual wonder board. Some leaders abilities are obviously stronger than others, so if you get stuck with some crumby leaders you'll be at a big disadvantage throughout the game. Lots of new icons to learn on all of the leaders cards as well.
I could take or leave this addition to a game of 7 Wonders.