I keep noticing no one is getting the Norman Bates homage. I love that Sylar is turning that around and making it freaky psychotherapy. Anyway, I'm sorry one of the originals is being killed off. Even those most badly handled by the writers (Peter, Mohinder) are redeemable; it would fit in with the "Redemption" season theme.
I hope Hiro's 2nd big story arc works out better than the first, which was just too far removed. We'd all love to see him become that cool ninja warrior, finally. It does look like the Big Split with Ando is imminent, though. Bummer.
My take on why Sylar wasn't killed by Danko's knife is that the DNA reshuffling has messed with his structure. But what I want most of all is for all those emotional appeals from Elle, Luke, Micah and Mommy to finally turn Sylar toward his own redemption. They all seemed to chip away at his self-loathing. Maybe his presidential ambition will actually be for good instead of evil.
Last note. Claire is too young for Sylar! EEW. Give it a rest!