I haven't played 3.5 in over ten years, but I could still run you through a combat against some goblins or orcs right now, without any preparation. I can literally write down all of the relevant stats and abilities from memory, while you're rolling initiative, because it's all derived naturally from ability scores and class levels.
There's no way that I could run you through a similar encounter in 4E, unless I actually brought the book out and looked up their abilities. There's no way for me to guess what any of their powers were, because they were all unique to those specific monsters.
I've made monsters on the fly in 4e without writing anything down (i forgot to bring the monster manual). Including special abilities that where unique to that monster.
It was difficult, and I really should have at least written down at least the Defenses, to-hit, and HP, but I still managed it without any player noticing.
And that only took a year or so of playing.
For instance... just off the top of my head.
Wild-Tri-Elementalist Level 8
HP: 60, AC: 23, Ref: 18, Fort 18, Wis 22
Actions
Wild Blast: Roll a d6
1-2: 12 vs Ref: 2d6+5 fire damage in cone 5. Ongoing 5 fire damage (save ends).
3-4: 12 vs Fort: 2d6+5 cold damage in cone 3. The area is difficult terrain until the end of your next turn.
5-6: 16 vs Ref: 2d6+10 lighting damage in a line 10.
Reactions
Sudden Burst: When you are hit by an attack, roll a d6
1-2: 2d6 fire damage damage in a burst 2.
3-4: The attacker takes a 5 cold damage and has -2 to attack and defense until the end of your next turn.
5-6: Teleport 5 squares.
If I could pull making up monsters like that in PF2, that would be great.
*(It's been a few years, so the numbers might be off a bit).
Fourth Edition had a lot going for it. I'm a big fan of the precise language and AEDU. I'm a huge fan of the multi-classing rules. The unique monster rules were, by a wide margin, the weakest part of the system.
I disagree.
Well... I like the precise and concise language, and like the multi-class rules (though perhaps a bit too costly) and hybrid rules. I also liked the attacker always rolls (i.e. wizard rolls 1d20+int vs dex for fireball).
But I also really liked the monsters were more than just damage + hit points. Pushing, stunning, zones, teleports, changing tactics when bloodied, and just more variety, in general, kept it from getting stale.
AEDU wasn't bad for a class, but it's not something I liked system-wide. Again, more variety would be good.