Some games have what I call “grabby”. That special something that makes you feel, viscerally, the desire to play them. For me, Dogs in the Vineyard has it. World of Darkness had it. It didn’t have it when I read it, but after playing it, Apocalypse World has it in spades. And I’m beginning to suspect that Becoming Heroes has it.
Rob Donoghue has recently mentioned that it takes more than being a great game to get a place in his collection. I think that, for me, grabby is part of this additional something. So what’s grabby? I doubt I can answer that, but I can at least explore it.
These different games have different kinds of it, to me. Dogs in the Vineyard makes me want to play it for the fallout mechanic, and so it makes me want to play conflicts and escalate them. World of Darkness is full of setting detail that I want to play off of. Apocalypse World has grabby setting and mechanics (though not crunch) in that you want to see how these characters put their mark on the world. Becoming Heroes does it with something I also see in Apocalypse World, which is a simple basic mechanic and lots of ways to tweak it per-character.
I think that part of grabby is the quality of being unfinished. A sense that there’s room in the setting/situation/motivation/mechanics quartet for you-the-players and you-the-characters to do something and make a difference. Alex P. has on occasion talked about how the warts (or proud nails, really) in Burning Wheel are part of what draw him to play it. The weird exceptions and border cases provide a kind of texture off of which to act.
And I guess that’s the other important part of it: act. For grabby to be really grabby, it needs to be something that you can’t do, entirely, in the comfort of your own mind. It needs to be something that requires the input of others and the weird surprises of a role-playing game story to come to life. This is why the weakest grabby of the ones I’ve mentioned is the World of Darkness one: I could tell myself stories in that setting and be about as satisfied. At the height of my World of Darkness playing, though, I was intensely interested in what these characters might do, and so I wanted to throw various things at them to find out. I was, in Apocalypse World terms, playing to find out, and being a fan of the characters.
This is what keeps a game from being doll-making, I guess: a sense that it is (almost) always unfinished, and that you have to act to see what comes next. I think that clear divisions of authority and total freedom to act within that authority help, because with those, you cannot just play out the story in your head, but need to see what curveballs the other players will throw.