Pirates could take place on a livable tropical world with a secret cave you can explore to set off the adventure. Could come with things people have been wanting like swimmable oceans, beach lots, maybe even mermaids. I can't see how mermaids would fill an entire game pack on their own so a pirate pack could be a good fit. I also want a tropical vacation world but wouldn't object to also having a livable one.
Secret agent/spy stuff would be my second choice. They could introduce freelance spies and private investigators with all kinds of gadgets for solving mysteries. The everyday to that job might be similar to the detective career from GTW, but there could also be a big plot with a few different endings that you could initiate when you wanted to.
