I was taken with the 7 Wonders game from the first time I played it. I really enjoyed the progression of the game and the fact that all players play simultaneously makes the pace wonderfully fast without sacrificing any depth. However, after playing a couple of dozen times the base game can become a little stale because the available options are more or less the same from game to game, with the exception of randomly selected Guilds in the third age.
The Leaders expansion addresses this problem head-on. In addition to increasing the number of available guilds, at the start of the game the players are dealt 4 cards each from a deck of historical leaders such as Julius Caesar, Leonidas, and Plato - each with their own unique benefits. Players draft these cards and keep their set of 4 leaders hidden. At the start of each age, a player can either play play a Leader for its coin cost at the beginning of each age, discard one of them for 3 coins, or play a stage of their wonder. The number of starting coins has been increased to account for the new costs. A good set of Leaders can be the foundation for an optimal strategy that can result in some magnificent scores, but playing those leaders can advertise your intention and result in the other players harrying your efforts before they come to fruition. It's more important than ever to watch your opponents.
7 Wonders hits the table very frequently in my game group. With the addition of the Leaders expansion, I expect that to continue for a good long time.