Despite some saying the modes of play sound too video gamey in their terminology, I like the concept. Because it lets the GM and players gloss over what needs to be glossed over, and focus on the important stuff. If you're in downtime mode, we don't need to know what happens every day. Also, it lets characters have time to age, instead of being 17 yrs old and 20th level.
I really like this new system of 4 levels of success & failure on saves. Mostly why I like it is for PC spellcasters. You won't have to waste a round on a spell that every NPC resisted. But for GMs too.. finally they can have lots of low-level creatures that mean something. So what if all eleven CR 2 creatures have a DC of 11 on their ability. Even if you save, you're still shaken, or whatever. Love it.
I like the new action economy because it allows for more design space than attack/move/cast without having to come up with complex interrupts and new action definitions. Should speed up play and simplify arguments. Should.
Resonance gives a boost to charisma and allows for more old school resource management style play. Also, makes it more of a difficult choice to dump stats than PF1.
Levels of success are a better narrative than binary. They also give more in the moment excitement to rolling. However, success being failure and failure being a success is worrisome.
Backgrounds taking over for traits will hopefully span beyond level 1. Giving a much more flavorful and interesting aspect to leveling up. A good way to mix crunch with fluff.