Grand Theft Auto may have cast the open world genre in its indelible mold, but if you want to boil the concept of GTA down to its root inspiration, you could do worse than starting with the movie The Godfather. The Godfather won an Oscar for Best Picture, planted its seed in popular culture for years to come and literally inspired members of the criminal underworld to organize their efforts according to the tenets spelled out in the script.
No matter how you slice it, The Godfather Made Things Happen. So while GTA may have moved in, made audiences an offer they couldn't refuse and taken over the open world racket, it's no surprise The Godfather has come back to settle the score.
The Godfather II is loosely based around the "modern day" events in the film of the same name, and takes place after the events depicted in the first game. If you're a fan of the film series, I recommend taking a couple of Valium before playing The Godfather II. While the game borrows heavily from the characters and dialogue of the film, all of the events you remember are slightly misrepresented here, with events taking place out of synch with the movie's timeline, and lines being said by characters who didn't actually say them in the film. It's a little headache-inducing, especially when there's no real reason for it.
Take for example, your interactions with Michael Corleone. The game begins during the famous New Year's Eve Cuban revolution scene, when Castro's rebel army forced the president of Cuba to resign in the middle of a giant party attended by wealthy American investors and certain mobsters named Corleone. Your first mission is to escort Michael Corleone to safety following the collapse. You even get to hang out with Michael during the moments just before all hell breaks loose. Unfortunately, you don't get to witness the "Fredo, I know it was you" kiss of death scene. That scene doesn't even happen in the game. What's worse, Fredo comes with you as you make your escape and appears throughout the game as a recurring character giving you missions and information. That whole betrayal/revenge plot point has been omitted entirely. In the game's version of the story, Fredo apparently did not break anyone's heart.
Aside from the story oddities, however, the game is about as faithful as it could possibly be to at least the general idea of the film. The same characters appear doing vaguely the same things (you even get to take an active hand in setting up Senator Geary for his wake-up call with a dead hooker) and they even enticed some of the original actors to come back and reprise their roles (although, sadly, not Al Pacino). If you haven't watched the films multiple times, you may not notice the discrepancies, and you'll definitely appreciate the attention to detail that is there. If your experience with The Godfather franchise begins and ends with the games, then you're not going to care. The story is on par with or better than some of the best videogame writing and along with the characters and fairly good voice acting, it creates a plausible world with which you can interact.
Gameplay-wise, the coolest and most innovative aspect of The Godfather II is "The Don's View". If you consider the portion of the game where you physically run about from place to place, jacking cars, whacking made men and blowing stuff up the "action" part of the game, then the Don's View is the "strategy" part. From the Don's View, you can see reports on your family's finances, manage all of your business interests, upgrade your family members' stats, hire more guards for your rackets, call in favors from well-placed individuals and look at a top-down map view of the various areas where your family operates and not only plan your next shenanigan, but send members of your family to defend your rackets against your enemies and even take over new ones.