I wish more video games would just end and then die tbh. I'm not a fan of the expectation that game series are expected to continue because all it does is make certain that at any point in the future it's gonna turn into major ass and not recover. Just let it end strongly.
I guess every series needs innovation to stay good, more of the same, even if it's amazing, can disappoint, like the meh Yoshi Island or NSMB sequils. Some series can innovate and still be good, like Mario or Zelda. It needs a new idea, not just 'it was popular'