I'm DMing a game of PF2e right now. Biggest differences off the bat are going to be the action economy is just 3 actions instead of move, standard, bonus. Most things don't have an attack of opportunity so it's strategically beneficial to move. If you roll 10 over your target it's a critical hit, if you roll 10 under it's a critical fail. This makes you want to "debuff" a target with things like off-guard and demoralized because every +1 raises your odds of a crit. There's a lot more numbers and a lot more things to do, but the numbers are tighter than DND so encounter building is way easier. You get upgrades and abilities at every level and pretty much every class is good and playable with very few exceptions.
I'll think of a sig later.