Orochimaru's entrance. What a fantastically creepy villain, and what an awesome nostalgia moment for me.
We also get to see team 7's genin fail, stand back up, shine, and eventually fall again. I love these rough patches. When these guys shine, they really shine hard. Sasuke was good, Naruto was better, but when Sakura decides that she's had enough, my heart really soars.
Sakura is kinda weak and only a little funny in all the manga that came before, being technically good but low in spirit.
That changes here, and how beautiful it is. :)