As for expansion packs vs game packs, I was very pro expansion packs when sims 4 started because I was used to EP's in previous iterations. But now I like game packs just as much or even a bit more . I think packs like parenthood and vampires have proven that interesting gameplay is not exclusively for EP's .
I think EP's are packs which takes up more resources to create the content, coding or animations needed for the pack. So Island living can be a EP because of the swimmable ocean and mermaid animation needed. But unfortunately it feels as if the team tried to take to many 'shortcuts' to implement a feature. I would be okay with a rabbit hole career, but not if it is sold alongside a rabbit hole cave and rabbit hole diving and no underwater world. And mermaids can't snorkel or climb a ladder out of the water because the team did not get to creating the necessary animation. I am glad I resisted the urge to buy this one full price. I will get it on sale.
I think this pack has more claim to the EP label than get famous because it at least adds something unique (unique to sims 4 at least) to the game whereas get famous was recycling a lot of features (fame looks like parenthood character values, the active careers use the framework set out by get to work, the perks are a rehash from vampire powers) and even the world was small with huge backgrounds but little usable space.