Pretty good episode O_O
But what intrigues me is that at one point, during a flashback of Halibel bowing before Aizen, you will notice that she was in full bone armor and looked completely hollowfied, save for a portion of her face. This was obviously not her pre-released form or her post-ressureccion, so I'm guessing that it was before she was an arrancar. Then, considering the humanoid body structure she had, that would make Halibel a Vasto Lorde, just as the top 4 are suspected to be.
Strangely enough, that part was not shown in the manga O_O