I also agree this episode was the best of the season so far.
I loved almost every aspect of it, by far Peter/Nathan together again was the best of the whole episode, and the ending scene almost had me crying.
I also loved the Matt/Sylar scenes and all four of them together was just as great as I hoped it would be from reading all the spoilers.
I liked Tracy and Claire as well. Good storyline without taking up to much time. And I wasn't feeling *so* much like "let's get back to Peter/Nathan".....
I liked Mohinder returning which I didn't expect, I think Hiro is a tool this season. He's become quite unpredictable. And while I get why he did what he did to Mohinder, I still don't agree with it.

I wanna like Hiro, I really really do, and he's had his moments. But right now I'm just like grrrrr.

. He went from being awesomely Heroic with some comedic relief, to be the annoying comic relief, to now being a tool who's only focused on getting Charlie back. It's just frustrating to me.
And I will agree some of Peter's actions seemed slightly out of character for him this season, he was ignoring Nathan at the beginning of this season. BUT on the other hand, he had to know how much confusion Nathan was going through. Nathan was uncharacteristically vulnerable with Peter last night, and I know in my own relationship with my sister, no matter what issues we may have with each other, in a pinch when we really need each other, we're there. No matter what, so in light of that, Peter isn't really acting out of character.
All in all, fabulous episode, absolutely my favorite so far this season and I have no doubts the next 2 possible 3 episodes will top it......