That age old question: Sequel vs. new IP - which is more successful and desirable, the tide seems to flow back and forth between them. On the one hand we want the new experiences and fresh milieus that a new property brings - however unproven game mechanics and unknown characters have a harder time finding funding, require more testing and might still in the end turn out to be unappealing, unrefined or simply remain unnoticed by their intended audience.
On the flip side sequels bank on a proven formula, a built-in audience and a safe established brand that is more easily green-lit by publishers and who's financial success is much more easily prognosticated. However sequelitis always seems to hit sooner or later, we've all felt sequel fatigue and many IPs struggle to retain their audience past the third game in the series.
Try as they might to breathe new life into it by "remaking", "rebooting" or "reimagining" a series - we are often left with something less charismatic, too different, too samey or just plain broken for us to care.
So what's a game dev to do? Enter the spiritual successor. Though mostly out of necessity and seldom by choice, these games still seem to be able to find that sweat spot between the fresh-but-unproven new and the safe-but-tired old.
Not bound by the fiction and characters of it's predecessor - yet being able to take it's successful mechanics, atmosphere and built-in audience - the spiritual successor can basically reboot an IP and create a new one at the same time, while gaining the good will that both are granted by their respective audiences.
BioShock took the cult following of System Shock and enticed the rest fo us with a new exiting IP. Harmonix reinvented the sub-genre of rhythm games they created with Guitar Hero when they split with Red Octane and created Rock Band. BioWare took what they'd learned creating Star Wars Knights of the Republic and made their own Sci-Fi universe complete with a myriad of alien races, good vs. evil choices and magic that is The Force in all but name.
Some devs have also taken to this practice by choice, giving us Shadow of the Colossus from Ico, Heavy Rain from Fahrenheit/Indigo Prophecy and Assassin's Creed from Prince of Persia and Splinter Cell.
Taking it one step further - Irrational Games is doing it again with BioShock: Infinite and there's Dark Souls - From Software's spiritual successor to Demon's Souls which in turn was the spiritual successor to the team's King's Field series.
Let's hope that we see more games created using this method if and when sequels can't do the job. What will respawn next, standing on the shoulders of their forerunners?...