I have very mixed feelings on this. The story is great from what I remember, not much a fan of replaying it but I don't think I've done that with any GTA campaign. The online however is what I'm going to be mostly focusing on here.

It's bad. It's boring, it incentivizes ruining other peoples hard work and god forbid you lobby up with a K/D warrior. Those people are strange. However if you host a private lobby with friends its actually pretty fun! Especially with the extreme amount of custom games the community has made there's a lot of room for fun in a party setting, if you're more of a solo gamer kinda guy I'd recommend just getting this for the story though, online custom games are alright but without friends it can get boring quick. Solid game though.