We do lots of different things in video games but every so often we find ourselves, controller in hand, experiencing one of those "this is why I play video games" moments. In 2010, the best of these came while directing Commander Shepard through conversations in Mass Effect 2. A refined version of the system in the first game, it perfected the ability to naturally guide the course of conversations being held by the characters without having to break and reason out long passages of dialog to select between. Coupled with greatly improved staging of the scenes and more cinematic camera angles, it became almost impossible not to get completely wrapped up in Shepard's saga.
Runner-up: Assassin's Creed Brotherhood
In an online world dominated by military shooters, Assassin's Creed: Brotherhood introduced a clever cat-and-mouse multiplayer game with a very different pace. It got players completely engrossed in trying to balance behaving in a way that avoids arousing suspicion while simultaneously stalking their prey.