I might get some disputes over what I am about to say, but personally I think it's time for The Undertaker to go. I think he's been there for too long. He is now 18-0 at WrestleMania, he's beaten people from Kane to Shawn Michaels, and even people from Triple H to Ric Flair. Yet he seems to just stay.
If you ask me, The Undertaker should have retired after WrestleMania 25. I think it's just his time to go. It's the thing every single time we see him. I think people are getting bored with seeing him.