My first (and only) PbtA experience so far was running Masks for a bunch of players who had also never played any PbtA.
Before I go any further, all of the posters here gushing about how good Masks is? Amateurs! It's even better than that.
I had to unlearn a lot, and I'm still doing it. Now, even with traditional games I do a lot of improv - that's not the unlearning. This game might be easier for me to run if I hadn't so many hours of traditional games because some of the base foundation is different. "Play to find out" sounds like a snappy sound bite. It's not, it's a diamond core.
And the focus is something I had to unlearn. I've played a number of superhero systems over the years, with over a decade with actively playing HERO - the most numbers forward, can model everything, super hero simulation.
Masks doesn't really care about that more than the player and the GM have a reasonably aligned idea of what your power can do under normal situations. Masks when you "build your character", you aren't picking a
class or something that is about primarily the features and abilities of your character. You're pretty much picking "what type of teen superteam angst am I most interested in investigating", with a side of who you are. Are you The Janus whom juggling your secret ID and "who am I really" at the forefront? The Doomed where doom literally is coming for you, and pushing your powers will hasten it just as mucha s give you more to do good with in the meantime. The Legacy, latest in a long line of heroes to live up to - or not? The Deviant, The Transformed, The Nova, and so on.
Remember when I said what you could do under normal circumstances? Want to beat up a goon using your powers? Know what you roll? Nothing - you succeed. You're a super, he's a goon.
On the other hand, does your Nova want to push her plasma control power to suck the fire out of the burning skyscraper - without killing all the people in it? Oh yeah, now it gets interesting.
And the same for the players in terms of unlearning. Relationships are a big deal, and in a teen super team there are times you'll be yelling, arguing, and storming out if it doesn't devolve to punches and lasers. You know what, that's okay. Death isn't on the table, the consequences of this add to the fun and the narrative unlike in a mission-success-forward game like D&D. Split the party and explore two different parts fo the villian's lair to try and find the hostages - it's okay. Basically, so many things that are verboten as "worst practices" in other RPGs are fine here.
And that's because the narrative you are developing together is the measure of
player success instead of player success often feeling linked to character success like in more traditional games.
Masks gives fantastic GM rules - not advice, but rather goals, principles, and rules. I've read Apocalypse World and as the granddaddy that's it's legacy - it gives fantastic guidance to the GM how how to run a very particular game incredibly thematically.
And the games are more focused. I don't know if I could see a "big tent" PbtA - and if it loses that hard focus into creating playbooks it would lose a lot of it's appeal. For as much as I like Masks, I wouldn't use if for a general supers game, it's fine tuned around finding out about who you are as a teen super, when your friends, mentors, the public and even your enemies have their own views on who you should be.