It's fun when playing with friends. The difference between playing by yourself in a free roam and playing with friends in on is remarkable. Multiple hours of fun just by driving around and killing people, starting mini-wars between everyone, killing each other, etc.
It's basically what we had to do on GTA IV, which is where the disappointment comes in, because there was supposed to be so much more to do on "GTA Online". They gave it its own name-- not GTA V Online-- because of how big and expansive it was going to be.
I have patience but not optimism as Rockstar's main focus just seems to be on making it as hard as possible to make money, forcing people into buying GTA$. At least on GTA IV when my friends and I messed around like we're doing now, we didn't have to make money to pay for guns, ammo, insurance bills, etc.
Overall I'd say it's not close to being a failure yet, but it's on the verge of being labeled a massive disappointment. It's getting to the point where unless I have a ton of friends on, I'd rather play story mode, and that was never the case with GTA IV for me. The story mode itself had me somewhat disappointed, but I figured online would redeem all of that with the ability to do whatever, whenever.. and it just hasn't happened yet.
I thought the game was an auto-lock to be a 10/10 and win GoTY, but I'm starting to think otherwise.