...7 Wonders: Babel in 2014, and unlike past expansions this one contains two separate elements that can be used separately or together or in combination with any other expansion.
First, players now work together to build the legendary Tower of Babel. Okay, work together is a bit strong as you're not necessarily trying to help another; in fact, as you build the tower ideally you're hurting others at the same time that you help yourself. At the start of play, players are dealt a hand of tower quadrants, then (since this is 7 Wonders) they draft quadrants: pick one, pass your hand, pick another, etc. During the game that follows, you now have a fourth possible action: Discard a card to build a quadrant, scoring 2 VP for the first you play, 4 VP for the second and 6 VP for the third. Each quadrant has a law on it, for example, each player has access to a particular resource each round, or certain resource cards don't work, or military victories pay out differently; this law affects all players until it's covered by another quadrant, but (since it's a quadrant) it can't be covered until three additional quadrants have completed the bottom level of the tower and it's time to play higher up. If a quadrant hurts your normal style of play, be sure to draft it and sit on it!
The second half of 7 Wonders: Babel consists of, if I recall the right word for it, agreements between various groups: trade agreements, military agreements, etc. What this means in game terms is that at the start of each age, you draw one card from the appropriate age agreement deck and reveal. A certain type of cards (commerce, military, etc.) now has an additional cost to be played. If you pay the cost, you take a marker from the agreement card, with the number of markers being one less than the number of players. If at the end of the age, all of the markers have been claimed, each player with a marker gains a bonus for each marker owned; if at least one marker is still on the card, then each player without a marker is punished in some manner.
I've played 7 Wonders: Babel once, and it's a great twist on the game for experienced players as you need to reevaluate everything to find out anew what's best to do with what you're grabbing from the ages. Knowing which quadrants you have in hand lets you plan for how to use them best, but then you need to spend a turn activating that quadrant and can you really spare the time to do so when you want to do so much else?!