**GTA boringness factor: when a game is fun for the first 2 days of playing it and then it's ready for the recycle bin
I wouldn't describe that factor as being inherently GTA. GTA and VC both lasted quite long for me naturally due to their open-ended play (There just came a time when I felt I had done everything that I wanted to do, so I deleted them.)
I'd say what you have described is actually the defining factor in every game with a linear storyline, Mafia included. Unlike GTA, Mafia actually didn't offer much of anything outside the main storyline.
While you are given the opportunity to roam around Mafia's city (Can't remember the name), there just didn't seem to be any clear incentive to do so. In contrast, not only did Liberty and Vice city offer spectacular rewards of sight and sound (explosions, gore, etc.), it also incorporated a comprehensive rating system.
Of course, going back on topic, with it's myriad of possible player-created situations GTA could never have related a cohesive and properly paced storyline to the player.
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