A couple of pros for Island Living:
- Island living has a world that changes dynamically with your actions, although only for the better, never for the worse, and the changes are rather subtle.
- The conservationist career is fun and has a real impact on your game with the global policies you can pass later (for example makes food prices rise or grant sims a monetary nonus when fishing invasive species out of the ocean).
- The pack introduces odd jobs that are available in every world, not just the new one.
And cons for Seasons:
- Climate is fixed per world, you cannot decide yourself
- There are only three possible lengths of seasons
That said, you can't really go wrong with Seasons. Myself I got it last, first experiencing the gameplay of the other packs and then rediscovering all the worlds with Seasons.
