I thought S7 was better than it gets credit for, but the biggest problem this series has is that it has created dramatic tension through putting Dexter in more and more precarious positions. If rule #1 of The Code is "don't get caught" and Dexter knows that LaGuerta believes that he killed Jimenez, why would he go after Estrada?
In cases like that he acts with an impulse inconsistent with the character's belief system. I know it was done for the purpose of creating the dramatic tension seen in the season finale, but it wasn't well done.
Oh, and here's how I see this one ending:
Zack kills Dexter, Deb kills Zack, Deb adopts Harrison.
Die, Steckel. Die.