As Obi-Wan's cuts off Anakin's legs and Anakin rolls downhill, it seems as though Obi-Wan wants to help him but stops himself (0:51). After he realizes Anakin is now Vader, he pulls himself together, only to have the well of emotions errupt.
We all know Anakin feels remorse for his dark deeds, because we see him crying after the seperatists are eliminated. However, I see more of this on Anakin's face as Obi-Wan is explaining his disbelief (1:13). It's like good and evil are battling within him (Sure, it could be the pain of limb loss and raging heat, but I see emotion there). Then Obi-Wan turns his back on him, collects his saber (This weapon is your life!) and starts to walk away. Seeing all of this, no doubt, allows evil to win.
He screams "I HATE YOU!!!" (like a pissed-off teenager to their parents), and right after he says it he has a look of disbelief in his own words (1:34). What makes the whole scene, for me, is when Obi-Wan says "You were my brother Anakin. I loved you." which, partially due to the music, makes my heart sink through the floor everytime.
Lastly, I think Anakin is reaching out to Obi-Wan for help, and not just trying to grab higher ground (2:08).
This is how I've always thought of this movie, but I've never been able to say it so eloquently. Nicely done!
