I would guess... making Paladins no longer able to nova smite? Maybe making TWF semi-decent again?
Honestly, most of the changes I really like are balanced by changes that feel like shuffling deck chairs. They barely touched spell balancing, and walked back a lot of changes that were nerfs because they were "unpopular" -- which, of course they were unpopular -- even though they're kind of fixing major issues with the design of some game elements (polymorph, summoning, etc.). On top of that it feels rushed. If anything, it's simply more clear that you're not really intended to feel strongly about it one way or the other.
I'll pickup the base 3 books, and probably continue to play when it's not my turn to GM. But I think I'm either going to favor Shadowdark or Draw Steel going forward when it's my turn to run.
It's fine. It's marginally better than the game from 10 years ago that had millions of people playing it and finding all the warts. It's definitely not $150 better, and it certainly hasn't convinced me to re-subscribe to D&D Beyond. Especially because I tried making a character and immediately found bugs.