What should have been included in 1E's UA that wasn't in there?

[RFisher]

But that's presumably only because you've already sacrificed Greyhawk Adventures, Dragonlance Adventures, Oriental Adventures, and Manual of the Planes, right? Surely you don't consider any, much less all, of those books more valuable/useful than UA?!

I've never owned MotP or the Greyhawk or Dragonlance books! I do remember considering the latter two many times. I don't think I ever even considered MotP because (1) planar travel wasn't that common in my groups & (2) when it did come up, we prefered to make up that stuff ourselves.

OA is my most recent & my only second-hand oAD&D hardback. So, it's position in the order has less to do with how useful or inspirational I ever found it in actual play.

Though, even if badly done & never used, I think I generally find the idea of a "AD&D adapted to a different culture/genre" more interesting than "a bunch of new races, classes, &c., &c. for AD&D".