I haven't been a fan of PbtA for reasons similar to those Bill articulates - but I recently listened to
the Esoteric Order of Gamers' playthrough of Monsterhearts and for me that made rather more sense of it, and of "narrativist" games in general.
In my standard mode of RPGs, each player gets into the mindset of their character. Here's a challenge - how am I going to resolve it? When I run or play GURPS I rarely see players rolling for their disadvantages, unless they want a hint from the dice ("would I be Lecherous
here?"), because they've already internalised them.
In PbtA if you try to play that way you'll be constantly kicked out of it. This game is not about thinking like the character – it's about being the writer on the team who has primary responsibility for that character. You're not trying to get them to their goals, the way they would be themselves; you're trying to get them into situations that will let them show off their distinctive traits (both good and bad), and to make sure the overall story is an interesting one.
So I think it is worth laying that out for the players up front and making sure they're up for it. And then pick the right game, because as Mark suggests each game is basically more like a short campaign in scope, not a full-on play-anything-in-that-world RPG.