One aspect of gaming I've always been particularly fascinated with is metagame. Metagaming involves following trends and balance issues in highly competitive games in order to keep the competitive edge. Metagaming can be more broadly defined as using any strategy found outside of a game world. For example, looking up strategies online is metagaming because the player has access to knowledge that the game character does not.
One of the best examples of metagame is found in StarCraft II, in which players can guess at opponents' moves ahead of time based on which units and buildings the player is focusing on. (This is why StarCraft veterans won't stop harping on you about how important it is to always scout your enemies.) Because certain strategy types become popular, players who want to stay in the upper ranks will keep on top of which strategies are currently the most common. Recognizing these strategies and learning counters to them is essential to keeping up a good win streak.
However, often players will create deceptive scenarios that make it look like they are about to make one move when actually they are planning on doing something else. The opponent, who is expecting one strategy, will be taken off guard when an unexpected strategy comes into play. This keeps the metagame evolving, as players need to always know which strategies are currently popular and which have become so easily counter-able that they're now obsolete.
Being a good metagamer is essential to performing well in a lot of highly strategic games. But is metagaming dying out? Currently, games that are much simpler and have virtually no learning curve are very popular, and these are also much cheaper to produce. For example, those of us who love Angry Birds can just sit down and play the thing without having to think too hard about strategy or metagame.
Creating a game that incorporates a strong metagame is difficult. Highly competitive games require insane amounts of fine-tuning so they remain balanced. One character or faction cannot overpower another, yet each must function and play in entirely different ways. Great deals of time, energy, and money must be invested in order to maintain this sort of balance.
I sometimes worry about the death of metagame. Is it really worth the effort to put so much work and testing time into a product when most players will move on to another game in a couple weeks anyway? Isn't it easier to make and maintain the next Angry Birds than the next StarCraft?