Gameplay is a big category and there have been some standout experiences this year, with interesting new mechanics and significant impact on players, but for me, the most impressive was XCOM: Enemy Unknown, the strategy title from developer Firaxis and publisher 2K Games.
XCOM is a game of two layers, a strategic one that deals in high level choices linked to both characters and items, and a tactical one, where the player actually directs a team as they battle the alien invaders.
The beauty of XCOM: Enemy Unknown gameplay lies in the way the two layers interact with each other in interesting ways.
Taking too long to set up research infrastructure will mean that a player is under-armored and under-armed on the battlefield, which can lead to more losses among the precious soldiers, but does allow for resources to be diverted towards more satellites and greater income.
Taking risks on the battlefield and moving to capture rather than kill aliens will once again lead to more losses but will speed up research and might deliver crucial resources that will make the middle and end game easier.
Add to this the special terror and abduction missions that can change the course of a campaign, the all-important Officer Scholl and its expensive upgrades and the various Council requests and you get a single-player focused experience that stays interesting and surprising no matter how many times a player experiences it.
The tactical battles of XCOM: Enemy Unknown might seem more limited than those of the original from the ‘90s, but Firaxis does a great job of making the game unpredictable, with class choices and equipment creating a horizon of possibilities that keeps players on their toes, both tactically and emotionally.
The only valid critique for the core mechanics of the game is that it’s much too easy to get into a death spiral that’s impossible to get out of, but difficulty has always been a selling point for the series.
Here's a full Softpedia review for XCOM.