Temperature and humidity sensor is a nice perk for those of us with acoustic guitars and orchids. Presumably it can be used with Apple Shortcuts to trigger notifications. Might upgrade my first gen HomePod eventually, but it still sounds great.
Also see the comparison table at the bottom of this page: https://www.apple.com/uk/homepod-2nd-generation/
Maybe the update also requires iOS 16 on a connected device, I’m still on 15.