5. Upgrades
One of the most satisfying things (for me at least) in a single-player game is watching your character grow, whether it be in physical appearance or just with stats. It's always rewarding to feel as though you're constantly making progress and becoming more powerful as you play. GTA V should implement this in some way. The various stats CJ could upgrade in San Andreas were... interesting, but I think that being able to improve your proficiency in areas like shooting, stamina, and maybe even personality would be really cool. Sex appeal just isn't something that should really need upgrading. Especially when you have money.