I might be in a good position to answer that, since I'm currently GMing PF2 as well as DMed two short 4E campaigns in the past year.
I'll make a (noncomprehensive) list here, and if you need further explanation of any point, let me know.
Compare
- AEDU Design: With the exception of a few daily resources (spell slots), many powers can be regained after a 10 minute break: focus spells, focus points, using nonmagical healing checks, etc. So this allows parties to conserve resources and spread them out but otherwise take each encounter as a fresh experience.
- Skill Feats: These work like utility powers. You need to expend a feat selection to attempt certain skill uses.
- Reaction powers: The reaction resource (normally attacks of opportunity in PF1, 3.x, and 5e) now have many more uses. The Champion's reactions set him up like a 4E-style defender, for example.
- You Don't Have to Have a Cleric: Healing is really spread out, especially with the Medicine skill. In Exploration mode (outside of combat), you can basically heal up to max HP between fights without expending spells, Hit Dice, etc.
- Critical Hits: Deadly weapons (which deal extra bonus damage on a crit), magic weapons that deal fire damage on crits, and other features make criticals mean more than just "I roll extra damage"
- Positioning: Combat maneuvers (which can also be put onto spells with a feat) let characters control the battlefield, shoving, tripping, sliding, etc.
- More Front-Loaded Power: Characters at lower levels have more HP and access to more abilities than their 5e counterparts, seemingly closer to the power level of low-level 4e characters.
- Ancestry/Race Powers: Your ancestry feats seem closer to how 4e handled race.
Contrast
- Encounter Design: Doesn't have the same "encounter budget" formula
- Minions: There are no minions in PF2
- Monster Spells: Enemies use spells and feats much like PCs. They don't have simple "powers" and you have to look up everything in the Core Rulebook.
- Conditions: PF2 has many, many, many conditions, and they are handed out like Halloween candy. I feel like 4E gave out a lot of conditions, but they had similar effects.
- PC Options: The PF2 Core Rulebook player options are vastly more than the 4E Player's Handbook 1.
- No bloodied condition
- Monsters aren't easily modified up or down in power, still require templates, etc.
Thanks for this comparison -- I've never played D&D 4e myself, but I've heard people talk about it, so I found this compare and contrasting very interesting.
- Conditions: PF2 has many, many, many conditions, and they are handed out like Halloween candy. I feel like 4E gave out a lot of conditions, but they had similar effects.
Aside: While it's true that PF2 has a lot of conditions, I think a lot of this is just a consequence of the designers getting "key word happy", not an indication of the complexity of the game.
For example, several of PF2's "conditions" are just descriptions for varying degrees of being hidden -- "undetected", "observed", etc -- which could have just been kept in the stealth and perception sections. Several more of PF2's "conditions" are just descriptions of a creature's attitude with respect to diplomacy -- "friendly", "unfriendly", "indifferent", etc -- which could just have been kept in the description of the diplomacy skill. But putting them under the list of "conditions" for reference doesn't actually may the game any more complex (though it does make the game look more intimidating).
To put it another way, I think everyone will agree that D&D 5e does a great job of streamlining conditions. But most of conditions PF2's conditions also exist in 5e, it's just that many of them aren't given a specific name or listed in the "conditions" section.
For example, 5e has an analog of PF2's "dying" condition -- in 5e it's the number of death saves failed -- it's just 5e (reasonably) didn't bother giving this a special name. In 5e the conditions "lightly obscured", "heavily obscured", "unseen", "lightly encumbered", and "heavily encumbered" all exist, but 5e (reasonably) doesn't bother listing them in its list of conditions.
And most of the other PF2 conditions that don't appear in 5e's list of conditions still exist in 5e, but are just described under the relevant spells that bring these conditions about instead of being given a special name. E.g., the spells Confusion, Fear, Ray of Enfeeblement, Enthrall, Slow, Haste, etc. describe the analogs of the PF2 conditions Confused, Panicked, Enfeebled, Fascinated, Slowed, Quickened, etc., but just don't give them special names.
I think overall 5e's approach is better -- it makes a game that's more accessible to new players. But PF2's decision to "code" everything doesn't actually make PF2 any harder to play. It just makes it more intimidating to new players.