Since I spent most of my review of Part 1 of the season closer talking about Amy Acker (and there are worse topics to devote a review to) I want to talk about the writing team in the final-final.
First, overall, a fun-filled ride but somehow disappointing when considered in light of the expectations set in the first part.
Nothing technically wrong, mind you, but overall in the tone here I am reminded of Ron Howard's Angels and Demons, which was one of his most technically perfect creations yet also perhaps his most flawed because he got completely lost in the material.
Which brings me back to the writing team.
I notice that another IMDb member has already commented that this finale is not typical. And that of course is the point.
What deserves mention is that that the writers set themselves a great task. To use backstory not merely as filler (which, by its nature, it is) but to develop anticipation for what is to come.
If you think that is easy, try it yourself.
Or, better yet, watch any random episode of ARROW where the writers consistently shoot themselves in the foot the moment they drag out the flashbacks.
Sometimes you have to judge the achievement by the intent, not the result.
When you realize what a lofty goal the writers set for themselves, you also realize that they largely succeeded. And deserve acknowledgement for that.