The time. For a full game that seems really short.
Since when? For a non-RPG it actually clocks in a tad longer then most games. Almost every game I've played in the PS2 era on, unless its an RPG, usually takes 6-20 hours long, for an initial playthrough. Its one of the reasons my wife loves me having Gamefly (prior to pc deals) and hated me buying games, I would beat them in a day or 2 and move on.
Action games (DMC, Infamous, Bayonetta,GTA) average take about 6-12 hours to beat, same with most FPS.
RPG's take 20-100+ hours.
Now mind you these are initial playthoughs, where you may be learning the game etc, not find everything, and most of the time dont spend time grinding. Sequential plays yield lower times because you dont have to relearn anything your used to it. Even on the harder difficulties mostly.