I found this episode to be surprisingly enjoyable. I had low expectations, but they were more than exceeded.
So much so, that I want two spin-offs: Midvale with young Kara and Alex in their gorgeous forest / lake house as they grow up together and have various adventures. And some kind of happy Thelma and Louise (Alex and Kara) esque adventures where they just road trip around the US (and the world) in Jonns car listening to pop music, saving lives and leaven broken hearted men and women behind them.
Jonn was oddly cruel in this episode. Ill blame his Martian upbringing / exterior, but being a mind reader he should have known how painful it would be for someone to see their dead mother! Even if he cant read Karas mind, surely he should have known how messed up it was based on his past mind reading of humans. I can kind of understand him wanting to immediately emotionally impact Kara, but it was still a bit harsh.
And US schools are damn confusing. So, 15 to 17 year olds are all in the same class! Im guessing that Josie was held back a year and maybe Kara was ahead a year, so they were both in Alexs school year. Then again, I cant remember how much older Alex is mean to be. Maybe Kara had skipped two years ahead to be in class with Alex and Josie, although she didnt seem to be doing well in history.
EDIT: I hope they use the actors playing the younger versions again. In particular, I would like a flashback episode which better explains how Kara went from wanting to be a superhero when she grew up to refraining from being a hero for almost her entire adult life.