While I don't have Island Paradise, I do have Sunlit Tides and it indeed feels different from what I've seen of Isla Paradiso. Different terrain sculpting, lighting, real-life inspirations (South Pacific vs. Spanish/Caribbean), fashion, activities, etc. It's worth it if you really like island worlds.
I haven't played in Midnight Hollow much, but I love what I see so far. If nothing else, all the new CAS content with it is top-notch.