Not a good introduction to the series. It seems like they want you to think this series is about a fast-paced post-apocalyptic alien invasion by adapting the last arc. This is far from what the series is actually about. You can read the synopsis of the main series to see the difference. Despite avoiding the original 'slice of life' start of the manga, they instead give you exposition dump about many things you never see before in this episode. Seriously, there isn't much value added by having this in animated form. Early episodes should give people an idea of how the entire series will be, andI think this episode completely fails to do so. I would recommend people to skip this and go straight to episode 1. You didn't miss anything.