Can I just say compliments to the author. Great adventure. Going to squeeze it into my campaign somehow. Can I ask - are you a Planescape fan?
I can't speak for Chris as to whether he's a Planescape fan, or a fan of planar material in general (I don't know if he's here on the forums of not). But I am, and several of Diplomacy's more gratuitous winks, nods, and references to Planescape stuff boiled out of some suggestions I made during the editing process (except the modron which was James's edit from an original zelakhut).
But, that said, the module itself was already about as planar as you can get, and a very fun module at that (Sharlocke was an interesting character, and the mercane corrupted by a chaotic artifact was quite unique). I just had a minor hand in checking the manuscript for its planar lore in general, and adding some overtly Planescape references as they might apply.
I'll second your enjoyment of the module, Chris did a really nice job and it was a pleasure to look over it :)
Should go without saying, me being a planescape nut and such, but I hearby third the love for diplomacy.