I'm a person who relaxes when she sees her sims swimming in the ocean. I really liked that in TS2 Bon Voyage, so I had wished for a pack like this. The beach activities are fun, the island spirits are spooky and mermaids cool. I still haven't had time to try the careers or elementals, but I'm getting there.
There could have been more depth (I wish mermaids could actually kill sims, the volcano doesn't seem to do much and there could be more surprises or things to explore, instead of rabbit holes and moodlet events, but I would like TS4 in general have more interactable surroundings). Anyway, aside of that I really really like the pack and rather spend my time playing it than talking about it :)
I'm still over the moon that I won the pack in a giveaway, because I really wanted it and otherwise I would have had to wait for a sale.