Most of the villains Kara has fought so far have been one-off alien threats that attack the city, are defeated, and then never show up again. That's standard for a monster-of-the-week style format, but these villains don't tend to have a lot of depth or impact. There have been two exceptions however. Astra, Kara's aunt and a Kryptonian general and eco-terrorist who believes that human beings are incapable of keeping their own planet in check, and Maxwell Lord, a business tycoon and mad scientist who the show seems to be setting up as Supergirl's own Lex Luthor style nemesis. They're both interesting characters, but the show hasn't quite used them to their potential yet. For example, Astra was killed off long before she really should've been. It was a well shot, dramatic moment, but it came about a season and a character arc too early. In that same light, Maxwell Lord is slowly being built up to be Kara's true nemesis, being responsible for many of the mishaps in the show with more villainous plans obviously in the works. It's a good start, but the show really needs to establish a firm big bad if the overarching story is going to have any weight or stakes.
