Island Living; is it lacking?

Very much so. Sulani is beautiful yes, but that's pretty much the only interesting thing about this pack. And along with that comes one of the biggest issues, in that a majority of the new features are exclusive to Sulani. Like the water and beach activities, which also have very little variety. The new traits are focused on the aspect of the island. The new careers are either rabbitholes or the repetitive conservationist career (again, only useful in Sulani) with little replay value. I've also heard in reviews that mermaids have little gameplay. If it were a gamepack, I wouldn't mind these things. But as an expansion, I expect things to be expanded beyond just the new world and for longer lasting entertainment.

City Living was done much better as a 'living' pack, imo. Yes, apartments and festivals are locked to San Myshuno, but at least you get notified when festivals are happening so you can go there if you want. And a lot of the new additions, like the new traits, aren't focused on San Myshuno as a location. There are elements of the city that you can bring elsewhere if you want.

As it stands, imo Island Living should have been a gamepack.