Honest question - What's so great about V21?

I see a lot of complaints in here about zombie behavior changes ruining stealth, sniping, etc. I'm introducing my son to the game and I thought drinking water was handled better in 20.7, so we both rolled back to that. I've played a little bit on v21, I just play vanilla, no mods yet. What is so great about 21? I'm just not seeing it.