Could never get into GTA Online. I would just end up driving around pointlessly, unable to find races, missions and things to do. And when I would finally find a race, I would get absolutley annihilated by people in faster cars. I joined a heist and it honestly sucked. Never saw the point.
Hopefully GTA 6 changes that
I didn't touch Online for ages, when I did it was to create a character. I walked around and thought WHY ? I would rather single player DLC continuing Michael/Trevor/Franklin's story. That said I did get into Online over the years, you don't really achieve much other than ranking up your online character and earning weapons/money/cars.
Over the last few years I've gone through phases where I'll play it for a few weeks, then give it a 4-8 week break, then jump back in (even if it's to play quickly and run into the casino, spin the wheel and see if I win the weekly prize car (I win it a lot actually lol). The missions can be fun if you run with a good crew, I've played a lot of them solo just to rack up my money. Lately when I've played it over the last few months I'm just running errands for my businesses and racking up more money for potential purchases.
I've got the GTA versions of the BTTF car, the 89 Batmobile, KITT from Knight Rider and a Ghostbusters car among others.