This episode debuted the Guardian, a character from the 40's created by Joe Simon and Jack Kirby in Star Spangled Comics. It was nice to see the nod to the comic on the truck sending intel to the Guardian.
Once again Supergirl ventures mildly into politics adding some global warming into the story line, where of course the anti global warming character is the sinister cretin. Fortunately, it's just a back drop to introduce the Parasite. He was really well handled until they turned him into a CGI monster. The CGI monster thing is overused in these shows. Sometimes it's okay, more often hokey. I prefer it when they stick closer to the comic book incarnations of the characters.
The coming out part of the episode was handled very well, in fact the whole development of the relationship has been well paced and kept my interest this season. I suspected Alex was going to get denied, in fact I could swear this has happened on other shows. But it was still really well done and credible. It's great how obtuse Kara can be, she's super powerful but still a goofy kid so often.
Having grown up on the Christopher Reeves "You'll believe a man can fly very gently" incarnation of the character, the decision to make Supergirl the most action pack busting-up-the-joint of the CW shows was a wise decision. The Super Family is nothing but a bore when played as all powerful.