The second Civilization 5 expansion, Brave New World, competently expands the game and manages to add more without breaking anything that wasn't already broken. That said, nothing here fixes some of the issues that have persisted since the core release and the price tag is a bit steep for what you get. Most of the features are solid refinements but nothing feels terribly innovative. In the end, if you haven't put the game down since release or you feel the hankering to shape the globe a few more times, Brave New World is worth picking up.
The expansion adds surprisingly little to justify a $30 price tag. You get a slew of new leaders and units to play with, the cultural victory route has been significantly overhauled and linked the the new tourism system, a new victory type has been added through the world congress, and trade routes provide an easier way to spread influence and earn wealth... and that's about it. Overall it provides enhancement and refinement but doesn't feel groundbreaking enough to be worth your while if you aren't already sold on the formula.
The new leaders and units are all relatively ho-hum. You get the obligatory nods to the new trade system through some leader abilities and a few neat unit abilities can mix it up a bit at the various stages of the game. For units, the Indonesian Kris Swordsman who gets a random ability after its first battle and the Shoshone Pathfinder who is a scout/warrior hybrid that can pick its bonus when finding ruins are the standouts to be certain. For leaders, they all failed to impress beyond some of the modded ones I have seen with the exception of Venice. Venice is never allowed to expand beyond its founding city aside through the use of great merchants (of Venice) who can purchase city states and be puppeted into the empire. Playing as Venice dramatically changes the rules and is a decided breath of fresh air compared to the other leaders.
Culture in Brave New World has probably seen the largest overhaul. Culture now functions as defense against the competing tourism stat. Tourism is generated through expending great artists, musicians, and writers to create a great work that permanently adds to your points per turn. Tourism can also be garnered through exploring archaeological dig sites using the new, wait for it, archaeologist unit. If your empire wide tourism score outpaces every one of you opponents sufficiently a cultural victory is achieved. This resolves one of the major issues in that vanilla game in that cultural victories being tied to social policies seemed sort of odd. The tourism system now provides a much more intuitive path to cultural victory while simultaneously providing a viable option to defend against it.
The world congress functions as a fairly minor new feature. At around the mid-game, all players have the option to vote on specific global rules that can slightly alter the way the game pans out. For example, it is possible to vote on an army tax that will make supporting a larger army a bit more difficult or enact a world religion which confers a tourism bonus to those civs which have adopted it. None of the rules are terribly dramatic and they more function as a supplement then a game-changer. Every few turns a new rule can be voted on and, in the late game, there is the option to vote on a world leader who, if elected, wins the game. This option chiefly provides a victory path for those who want to play nice with city states as each ally provides an extra vote.
Tying all the old and new features are trade routes. Starting very early in the game, you get access to a trade route slot which allows you to establish relations with nearby cities (later in the game you can use trade routes to stretch much further). Each city that is affected by the trade route gets a bonus to gold income, a slight bump in science, a bit of religion spread, and a bonus to tourism score. The system is remarkably streamlined and is basically universally available no matter what type of victory you are going for (even warmongers can establish trade routes within their own empire for a tiny boost in income).
As stated before, none of the new features are sufficiently game altering to likely change your opinion of Civilization 5. Many of the lingering problems still exist (and at this point I venture are unlikely to ever be fixed). The AI is still inscrutably insane and is completely inept at engaging in hex-based combat. Defeat is more a result of losing to a cheating AI then superior tactics. The combat, even when not factoring the brutal AI, is still woefully breakable with battle feeling more like swarm and horde then Art of War. Finally, the boring strategy of spamming cities as close to each other as possible still seems to an optimal path to victory. If these problems were enough to turn you off in the first place then you definitely need not apply here.
My other primary gripe with the expansion is that it feels like most of the new features should have been implemented in the base game. The path to cultural victory always felt a bit contrived in the vanilla game and the tourism system directly addresses this. Why was culture so lame in the first place? The trade route system feels more like an extension of diplomatically trading luxury resources then anything revolutionary. Additionally, given that cities within your empire were already governed by trade connections impacting gold income the system, again, feels more like a refinement then something new. Finally, the world congress is neat and all but the diplomatic victory was already in the original game and was already dependent on befriending city states. The new world rules that can be implemented seem to be more of a bonus for players pursuing this path whereas previously they had little tangible benefit (beyond the city-state bonuses) for pursuing this path. Once again, the world congress acts as an enhancement to an existing system rather then creating something new.
So should I buy it?
All told, if the prospect of playing more Civilization 5 entices you, the expansion is worth the steep price tag to get the most refined version of the game. If you are on the fence and aren't particularly compelled to currently play the vanilla game then the expansion probably won't change your outlook. Lastly, if you haven't picked up Civilization 5 at all and are considering it, this expansion is probably a signal to wait for the inevitable discounted 'complete' pack to get the definitive game.