I grew up playing GTAIII. Since it was the first installment of the GTA franchise in a 3D environment, it was fun.
Replay value, there's a lot. More than what the previous GTA's had in the game. It's how you view your goals in the game, and how you reach them. If you expected way too much, then of course you'll be disappointed. I find that if you pay attention to the finer details of the game, that you start to appreciate, and enjoy the game a bit more.
Don't look at the bigger activities, and just judge. Learn that Los Santos has more to offer than what you previously complained in this thread. Compare the older GTA's to GTA V. There's wasn't much you can do except kill civilians or steal cars and evade the police. If you hadn't grown up playing the older GTA's, you won't really appreciate this one as much as some of us do.
Some people appreciate finding treasures, or exploring. That's their way of having fun. Don't just bash on them, or shove your opinions down their throats because you think a lot of the activities R* included aren't what you expected in terms of replay value/fun. Learn to adapt, and have some enjoyment with GTA V. If you think GTA V has cops which are annoying, or think every activity or mission is tedious when replayed, try playing some older GTA's. MP also adds replay value as well...