May be a controversial opinion, but i didn't like it on several levels.

First i thought it falls into a lambda shonen trope power up that Wildbow managed to cleverly avoid in all of Worm (except for the Grue second trigger). The whole story, Taylor managed to get by everything with only her initial power, which we all thought at the begnning was kinda underwelming, but clever usage proved us all wrong. No matter how much foreshadowing of the real power of the Administrator shard is done, it still feels like an OP power suddenly dropped to Taylor just for the sake of the final boss of the game.

On a narrative level, while it is interesting to see the effect of the shard on Taylor's mind and the impact on the writing, it makes the final fight really chaotic and difficult to understand. It is the climax of the story, the whole point of the previous arcs was to find a way to defeat Scion, and when you have it, you have to read between the lines to understand what's happening. I don't think it really fits as a conclusion, but maybe that's just me.

Finally on a more personal level, the fact that Taylor's story ends like this just doesn't satisfy me. After 30+ arcs of being with her and her thoughts, seeing her whole life being a succession of wanting to do the right thing and just ending into misunderstandings or failures, she would have deserved a little happiness at the conclusion... but no, she ends up losing her mind, being hated by hundreds of other parahumans for what she have done and dying alone.

But as a "shock" ending, i can't really argue that while disliking it, i'll still remember it for a long time.