Tracy walking away from the guy that was using her for his own nefarious political/personal ends was a big step up for her. She grew through all of her dying and killing and turning into water. And junk. This episode made her a lot more interesting to me than just as window-dressing for the show.
Hiro seems to be finally growing up a bit more, and I like that. I think that his selflessness (hero complex?) is melding with the newfound maturity nicely. I hope they don't kill him off.
I hope Mohinder has an option of coming back in as a one-shot from time to time, and that his actor wants to, occasionally. I don't think that they wrote him well for his entire run.
Nathan dead? Not cool. Adrian Pasdar is a good actor, and I like the interaction between his and Milo V's(not even going to try to spell that guy's last name!) characters. I think Sylar is going to end up with amnesia, because his entire personality was sucked into Parkman's head.
Speaking of which, power corrupts? But it couldn't happen to a nicer guy. Parkman, the real one, not the Sylar driven one, is such an everyman. He's just knockin' around, trying to get his act together, and some evil twood has to louse that up for him.