I liked Michael's story as well, the mix between him dealing with his past decisions plus trying to mend his relationship with his family was pretty interesting. Being able to call the other two protagonists to hang out while in free roam was also cool, especially since they keep the weapons you have on them.
The online is pretty fun now, I'd totally recommend trying it, especially now that most of the issues with it have been cleaned up and earning money is no longer a grind-fest. The multiplayer heists in my opinion are more enjoyable than the story ones, due to the fact you need to have close cooperation between the players, and everybody has their own job to do.
But I will say, the online community can be toxic at times