[MENTION=42582]pemerton[/MENTION]
I see "high concept simulation" and "narrativism" as a spectrum (to use Forge terms I really don't like), not radically opposed. Planescape does have a core concept - belief shapes the multiverse - but within that overarching concept there is a lot of room for a developing narrative based on emergent gameplay. If that feels too confining or too undefined/vague, then Planescape probably isn't a good choice. OTOH if you find richness toward the middle of the spectrum, then Planescape might be appealing.
If I may comment on the second part of this, in parallel with the "spectrum" conversation, for me it's like this:
Particular systems or settings don't
prevent any of the "agendas" being pursued - especially if they are modified by "houserules" and so on to fit the playing group's style better (a process called "drifting" on The Forge). So, Narrativist play in PlaneScape would certainly be
possible; I would just question whether it would really be
supported.
If you intend or desire to develop a dramatic theme, consciously, through play, why would you start out with a theme already writ large over it with the 'questions' predefined? Surely that predefined theme is only going to be a distraction, or get in the way, while the emergent development of themes that you are actually aiming at progresses.
Unless you are going to explore the predetermined issues of the setting, those issues just seem to be superfluous - a distraction from what is actually being attempted. Gamist play in PS hits the same problem; if the idea of belief isn't tied into the game system in some way, it's just a bit of "fluff" that is too complex for its own good.
[MENTION=71571]DracoSuave[/MENTION]
If rogue modrons aren't a reason to play Planescape I don't know what is. I mean they're just cute as a button, in an M.C. Escher-esque way.
Oh, yes - rogue modrons (in a Sim, exploratory sense) are way cool!
To be fair, it was also pre-Planescape
Certainly was - the "Deities and Demigods" and "Legends and Lore" books (1E and 2E) were the "culprits", mainly.