Before Watchmen

Earlier this month, as I was playing through Square Enix's Final Fantasy XIII-2, the appropriately named sequel to Final Fantasy XIII, I began to think about what makes a good sequel. When is a sequel justified? What does it need to bring to the table, in terms of innovation and new ideas? How much of the original needs to be preserved in order to stay true, and how much is just derivative? As these questions swirled through my head, I decided that my next post for UysFaber would be dedicated to the do's and don't's of making a sequel (from an artistic point of view, that is.