The Story offline makes so much fun that I've played completely within 3 weeks. My favorite character is Trevor. The scenes are (for me) really so funny that I have to also think and laugh because when the PS3 is no longer running. Simply delicious. In addition, you can empathize with the characters really well, which is not typical of an action game.
The long-term motivation is kept high by the very good online program. It's fun to work your way up through the ranks to be able to thus always buy better weapons to the ranks to come faster high. Really great.
If you like action games, GTA V is not to be missed. A great game.