Best episode so far, and one that didn't really suffer, IMO, from being aired out of sequence.
I have never seen the 1984 Supergirl movie or Helen Slater's guest tenure on Smallville, but did know who she is, so her recurring role in the series is exciting for me less because of nostalgia and more because of what her character's presence brings to the table in terms of narrative development, and I really liked the way they used her.
She played off of both Chyler and Melissa very, very well, and my favorite scene was when she and Alex have their 'truce' chat. For all of the 'pricklyness' of their interactions through a lot of the episode, it's easy to see that Eliza does love both Kara and Alex equally, even if she seemed to be far harder on Alex than she was on Kara.
I mentioned this elsewhere, but Kara uses the terms "adoptive" and "foster" almost interchangeably, and it's clear that she recognizes, appreciates, and loves Eliza for the ways in which she (and presumably Jeremiah as well) took care of her, so there's no disrespect being meant by her use of those terms.
Cat Grant continues to be one of my favorite parts of the show, and I love that her relationship with Kara is slowly evolving and changing. She does clearly care about Kara and her other employees, even if the way she that demonstrates said feelings isn't all that pleasant.
I don't know about anyone else, but I loved Livewire's look here and can't wait to see if/when she returns. I somehow missed her taunting of Supergirl during their third confrontation, but still loved the way they went at it. The effects during those sequences were great, and both the actors and stunt performers did an excellent job.
I have no idea where they're going with Hank Henshaw's character, but I like that Eliza doesn't have the highest opinion of him or his motives after losing her husband to the DEO, and that her feelings have been passed on to Alex and Kara, because it adds new layers of intrigue and nuance to their own working relationship with him.
It usually bugs me when things are aired out of sequence, but given the reasons for doing so in this case, it's understandable, and there really wasn't anything in the episode that was too jarring as a result of airing this episode this week instead of the one that precedes it.