Please allow me to echo all the other posters who called this awesome, and all the reasons they gave for that judgment. I loved this whole scene when it came out, especially because I love psycho-Huntress, and the crazier she gets, the more I love her.
That being said, I thought one of the most interesting things about this story is that, before this, Canary was only thinking about quitting the Birds, but almost right after, she announces that she's quitting, effective immediately. (I'll post scans, if people want.)
That's interesting to me, because this incident is, as far as I can recall, the first time that Dinah has really seen Helena's dark side. And look at the expression on Dinah's face in that last panel: it's plain just how dismayed she is by what she's seeing. So I wonder, to what extent did this incident finalize her decision to leave the Birds? Especially when you think about the conversation they have on the roof as Dinah was leaving.
Lastly, I'm glad we're having a Huntress is awesome week, because have I got some stuff to post.