I haven’t tried PF2. I‘d wonder how it compares to PF1 or 3.5e, but it looks like we don’t share those as common points of comparison. PF1 started up as a 3.5e clone, somewhat up powered - no clue what’s happening in PF2.
I've tried very minimal 3.5 sadly, but I'd be happy to answer any questions you have, feel to free to PM me, I'm as familiar as one can be through video games and osmosis.
Its d20 based, but it isn't a direct progression of 3.5 either, although a lot of elements will look familiar-- attack rolls, saving throws, etc. The designers have basically said its how they fixed everything that was frustrating them about the core 3.5 engine they had been dealing with for a decade. I would say the significant difference is that classes get a locked in progression of features that function to set their math up, but then have 'class feats' they choose every few levels in a lego-brick build-a-class approach.
Multiclassing and Archetypes, from PF1e are merged into one system where your base class math doesn't change from it (which means you aren't dealing with losing BAB or spell levels or whatever by multiclassing) and you spend class feats to pick up things from archetypes-- multiclass or otherwise, so for instance, fighter archetype feats make you more like a fighter, or you could take Shadowdancer for that kind of stuff, building it in feat by feat, or Dandy for social stuff, or caster to get light spell casting, and so forth, there's limitations so it functions like a big puzzle. The archetypes give you limited ability to do other class's stuff, a fighter with a wizard dedication doesn't give up their attack bonus, but they don't get a wizard's level of spellcasting bonus either for offensive magic (the game keeps them technically to the point where it could be useful, but you won't see many fireball slinging fighters as a matter of optimization, generally) but like... True Strike for instance? Great spell for a fighter to benefit from that way.
Finally, the game is harder and it has a more finely tuned balance than pf1e did, and tighter bands for numerical bonuses-- casters are about on par with Martials, and team PC will struggle without teamwork, which heavily emphasizes buffs and debuffs so people set up for each other. Crits deal double damage, and they happen when you beat/fail the DC by 10 or more (in addition to a 20/1 on the die) so the increased accuracy from teamwork translates into way more damage. The game has fleshed out exploration and downtime, that make it a total sleeper excellent system for some OSR styles of play, in my own opinion.
I think Morrus's review is actually pretty good too. We've gotten substantial amounts of support since then, which has really fleshed out the system's potential.
EDIT: OH AND 3 ACTIONS, its so natural I literally forgot about it, players have three actions per turn they can spend on stuff like 'move' or 'attack with a stacking penalty for each attack per turn' special attacks and spells take more than 1 action, so the game is super flexible about how you actually arrange your turn between attacks, spells, and various feats, and different classes and archetypes use those in different ways. I should also note Attack of Opportunity is no longer universal, instead being a feature, feat, or special ability for certain classes or monster-- which raises the value of mobility a lot.
(ducks).
