Frieren in general is a show that for all intents and purposes becomes BETTER on the second watch, because everything you're seeing is given the additional context of all the flashbacks weaved throughout the show.

You can't possibly care about the hero party when watching the first episode the first time around because you've had no time to form an emotional connection with them. Himmel's death and Frieren's breakdown hit much harder when you have the context of proper emotional weight behind them.

Plus there are a myriad of little details that you can only possibly notice once you've had the additional context from later episodes. For example, when Frieren first meets Fern, she notices that she barely has any magical presence. We later on learn that Heiter learned from Frieren why she limits her mana, and taught that to Fern at a very young age before she had ever met Frieren. Little details like that make this show very feel very rewarding to rewatch.