I get the 3 action economy is great
and that people t(Players like, me option but are they more than +1 and +2s?)
But what really is the gm part
how flexible is it to gm how fast can I adapt scenario or monster on the table based on player choices
how far and smooth runs dming
how easy/quick is basic prep
what is it about PF2 that would make me run it as a GM/DM over 5 I have little interest in being a player so it stands and falls with this
I'll do my best to answer (as someone who GMs a biweekly game that is currently at 8th level).
The adaptation part should be about the same as what you would do to adapt any similar game. You can use level-based DCs to set the challenge level for skill tests (or look in the rulebook to see if there is a specific DC). You get an encounter budget based on how difficult you want the encounter to be, but you can pretty much take the template of how many creatures and swap them out for the same level creatures. (Like if you knew the fight was supposed to be 2 level 6 Ettins but the group went in a different direction, find something else level 6 to replace it on the fly.)
I do next to no "basic prep." I run an adventure path. The monsters' abilities are all pretty much lined out in the monster entry. Roll dice and have fun. (There are a lot of conditions that get thrown around, so having the condition card deck has been very helpful to me.)
So here's what I like about it as a GM/DM (compared to 5e):
1) My players like it. Since they're invested, that helps me.
2) There is already close to as many options for monsters, spells, magic items, etc., available for PF2 than official 5e content, and...
3) It's basically free, using Archives of Nethys. You can search for any monster stat, spell, magic item, etc.
4) Every encounter is dynamic and interesting. I haven't had a bad one yet - in 8 levels.