They give you weekly challenges to complete to get you stars which are used towards the rewards for that season, each season lasts 10 weeks and then at the end theres usually a big change in the map/story but the maps evolving in real time throughout the season anyway. All that while being free (apart from getting the battlepass, which you can get enough points to pay for it through in game currency anyway just by playing).
First time i tried it was around october last year I think and like you didnt get into it. Was fun but nothing to go back to. Its that they keep adding so many things and they give you the progression challenges to keep going back and everything is sort of just discover and play how you want. Basically loads of fun and stuff to do if you want to just feck around solo or with a squad, but also if you want to play seriously.