Well session 0 crashed and burned due tot he complexity/layout of PF2 but I did enjoy some parts of it. Other parts are good in concept but need some work.
1. The Boost/Flaw system in character creation and level 5,10,15.
While technically the races have a flaw, in effect they do not as they get 3 boosts so you can offset it or in other cases mitigate it. This means its roughly the same as Pathfinder, 4E and 5E( well most races get +2/+1 similar idea). Flaws to strength mostly do not matter though if you are planning on being a primary caster.
2. All Races are good at something.
All races get a +2 boost to something. 4E and 5E to a certain extent often end up with very cookie cutter class and race selection. This is because its easy to start with a 16 using the default array but not if you do not pick a race that gets a boost to your classes primary attribute.
3. The Background system.
This is different to the 5E system and that is a good thing. Its a good example of more moving parts without increasing the complexity of those moving parts to much (+2 bonuses to attributes are easy to grok).
4. Breaking feats up into combat, skill feats etc.
This is not a new idea 2E AD&D did this back in 1989 *1E may have I'll have to check its WP/NWP). In late 2E an optional rule of character points feed the weapon and non weapon options from the same source. 3E went with feats but non combat and RP type feats compete with combat feats. 5E continued this with things like the Actor feat competing with Sharpshooter and Great Weapon Master (and less feats as well higher opportunity cost). This gives you options but flattens the power curve as those options expand the classes sideways rather than more combat power layered on more combat power (or pure skills if someone went that way).
5. Stats Above 18 increase slowly. Boosts above 18 only go up by one. This reduces the incentive to have a 24 (or more) whatever and have the rest of at 16 or lower. I suspect you will end up with a lot of PCs looking something like 20/18/16/14/12/10.
6. Unified Proficiency Bonus
4E had this along with 5E and Star Wars Saga edition. The +20 range might be two much IDK but since 2E AD&D some skills/proficiency have had combat applications but they advance at a different rate than THACO/BAB which creates problems. See for example 3.0 and 3.5 tumble checks or use the force skill in Star Wars Saga. Its also smoothed out things like SWSE and 4E +5 trained and +5 skill focus which combined with a 16 ability score creates a +13 difference in a non trained character with a 10 ability score. At level 1. I'm not sure +20 is a great idea though, 5E +6 over 20 levels might be to low.
7. Untrained- Legendary.
Ok a difference of +1 may not be exciting but it narrows the gap between an untrained character and a trained character to 5 points. Even in 5E with its bounded accuracy you can blow this out to a difference of 13 points (trained+expertise+20 ability vs no proficiency ability score 8. Combined with PF2's boost system and feat system their is also less opportunity cost to expand a PC into new skills. IDK if the numbers are right (trained to legendary each step is +1) but the idea is good. This is not that different to 2E AD&Ds system but you could go higher than +3 on a proficiency. IN practice you were better off getting new proficiency than a +1 bonus same theory probably applies here.
8. Max hit points via class and Racial Hp.
More hit points and less variance due to dice rolls but a bit more variance than say 5E optional fixed hp/level rule. See how this plays out but its interesting IMHO.
That is a few things so far. To me this means PF2 is not beyond hope. They can tweak or rewrite classes and tweak the math, hopefully they dump the PF2 round structure as well. How much time they have and how they fix things we will know at a later date the main concern is PF2 feels more like an alpha or beta test than a 5E type playtest.