I like when the spatial positioning of the characters in the fiction matters. "Now that you're standing on the monster's head, you have a shot to stab it in its unarmored eye and inflict a grievous wound! Well planned, well executed, bravely risked!"
I don't like when such relevance must be enforced by measuring the fiction in terms of game stats. "Standing on the monster's head gives you +2 for high ground, +2 for opponent's awkward defense, the eye socket is a -8 target, but the fact that it's a giant creature makes that -4, hmm, now that I've flipped through all these pages is there anything else I've missed?"
But I also don't like it when the group can't agree on how character positioning matters. Presumably, what all that statistical measurement avoids is this: "What?! I'm on top of the monster's head and I still can't stab it in the eye?!"
Of course, there are very simple social ways to solve this:
Player: "I'd like to climb onto the monster. Is that possible? Once I did, how hard would it be to stab it in the eye? And would that be a big deal?"
GM: "Not easy, but definitely possible! If you get up, the stab wouldn't be hard, but not guaranteed either. And yeah, a sword through the eye seems like a big deal."
But, if we were all awesome at that all the time, we'd probably all be playing freeform. So I'd like to talk about rules.
It strikes me that Apocalypse World-style outcomes have something to contribute here -- "you take definite hold of it" (e.g.) doesn't require looking up any modifiers or thinking in system numerical terms, but it's still a step above "see if the GM thinks it matters". (Probably. Right?)
So! What moves and other rules from AW-powered games do you like for this kind of stuff?