6. The Sims (2000)
As fashionable as it may be now to bash casual simulation games such as Farmville, few were casual about this, the game that popularised the genre. The Sims worked on a number of levels. Those looking for a quasi-RPG experience were satisfied, as were wannabe architects, wannabe sadists and wannabe gods. The Sims success can be partially attributed to this something-for-everyone factor, but what truly defined the game was the freedom bestowed upon the player to set their own goals and make their own fun. The influence of The Sims in this respect is refracted across the modern gaming spectrum, from the aforementioned Facebook fare to similarly open-ended titles such as Minecraft. The sociologically minded might be tempted to go deeper and attribute the popularity of the game to millennial technological alienation or some such. Really, though, wasn't it just plain fun to get them in the swimming pool and remove the ladders?