After some contemplation, I think I’ve figured out the crux of why Irene Adler’s portrayal bothers me so much: in the power play between Sherlock and Irene, it’s a matter of who has the last word, and who is silent.
In the original canon, after all is said and done, it is Irene who has the last word: with the letter she writes to Sherlock Holmes, keeping the photograph and sending him her self-portrait, she makes the final, definitive move against him in this chess game they play through the whole story. As a result of this, she walks away with everything she wants. She holds all the power in the end, and it is Holmes who is the loser in this game, as much as he admires her.
In the BBC remix, it is Sherlock, not Irene who has the last word in terms of power. John Watson said it himself, that Sherlock would outlive God in order to have the last word.
Yes, Irene brilliantly pwns damn near everyone in this episode: Sherlock, John, the CIA, even the whole British government. Had the final scene among Sherlock, Irene, and Mycroft ended before Sherlock cracked her passcode, it would have been yet another completely triumphant moment for Irene, akin to the earlier scene in which she drugs Sherlock and steals back the phone from him.
But what happens when Sherlock cracks the code is an utter inversion of power between the two of them. Yes, Irene set the passcode to SHERLOCKED (Was it indicative of her obsession with him? Done simply as a joke, another power play? Who knows?). But every ounce of protection she has secured with that phone is lost in that moment. It is Sherlock, not Irene, who gets to deliver the final, dramatic, farewell monologue. And what we are left with is Irene Adler, crying, begging for her life and protection. She is suddenly terribly vulnerable and exposed, both in terms of her physical and emotional safety. As Sherlock said to her regarding their game, “This is just losing.” When I say that she is broken here, it is the power she used to wield with that phone that is broken and silenced.
And even in the final moments of the episode, in the execution scene, it is still Sherlock that wields the final power over Irene, quite literally holding her life in his hands. She seems genuinely surprised to see him, and most likely would have died if he hadn’t been there.
It is this that bothers me most about the treatment of Irene: in the very end, she isn’t allowed to be the winner, with all the power and the very last word, as she is in the original story.
Part of what made Irene’s canon story compelling is not only did she have the last word, but she won her prize as a woman in a male-dominated society, which is an amazing victory. In the new version, even this victory—winning her security from all the men around her (Sherlock, Mycroft, the CIA agents, etc.)—is stripped from her.
Yes, I realize that the BBC series is a remix of canon, and that details are mixed and blended together to make someone new. Was I expecting an opera-singing adventuress? No (I was excited to see dom!lesbian!IBAMF!Irene in action). Was I expecting Irene to be perfectly canon-compliant? No (hell, John’s supposed to be married in this story, according to ACD, and there are plenty of other variants from canon).
What I was expecting, as with all elements of this series, was that Moffat tell the tales of these characters in the spirit of and honoring the essence of the originals. And when it came to a critical, important juncture for Irene Adler’s story, for me, that spirit and respect disappeared.
I have read other interpretations of this episode in which Sherlock and Irene are playing another power game with Mycroft in order to fool him to secure her safety: that the confrontation among Sherlock, Irene, and Mycroft was just for show, and that Sherlock and Irene arranged to fake her death a second time so that she would be free. I’d like to hold onto this as an alternate head!canon, because it beats the alternative for me.
Polite discussion is welcome on these ideas…thanks for reading.

This is how I want you to remember me. The Woman who beat you.
Irene Adler - A Scandal in Belgravia
(Source: hatingcoriander)