I'd say Call of Duty Black Ops.
The single player is unsatisfying but it's easy to get a multiplayer game with many involved, sometimes whole teams fighting for domination. Sadly some of those involved in the multiplayer can sometimes be underage... yet the box is clearly rated for 18+ only.
When it comes to playing a game there's many different choices of loadouts and equipment, giving you a tactical advantage on the battlefield. The gameplay is tense and frantic, not really allowing much time to camp so you have to run in for the kill.
Shamelessly well known, thousands of videos have been recorded of its gameplay and uploaded to youtube, some games are very satisfying kills while others are simply just griefing.
Possibly the most popular game around with those that play it, although since the title itself is rather average many wonder about its success and quite frankly... it's a bit overrated. Many other aspiring games copying aspects from it to try and make an impact on the multiplayer market yet fail to take away it's player base.
...yet those that only play intimate single player experiences complain about it all the time online.
I'm not even going to go into the zombie survival mode... yet playing with corpses can be a laugh.
Right... I'm all out of innuendo... I should just say "The Path"... no directions or clear goal in mind, but the experience has undertones of rape.