I thought there was a thread listing differences, but I havent found it yet. I did find this info relating to a Different Worlds article on D1-2

Descent into the Depths of the Earth - Greywiki
"Reviewer Anders Swenson reviewed the D1-2 Descent into the Depths of the Earth compilation in 1982 for Different Worlds #21. Swenson noted that standards for adventure publications had come to expect longer texts for the given price, so that the two adventures had been combined into one format; redundant text was eliminated, and new illustrations were added to fill the resultant gaps in layout. He was perplexed by all of the creatures found in the grand cavern area originally found in module D1: "All these creatures are apparently expected to do nothing but sit in their caves and wait to be attacked, for they would certainly defeat any moderately tough adventurer party specified by the author if they all tried a massed and well-coordinated attack." He also wondered about the placement of the kuo-toan shrine: "There is great hostility between the Kuo Toa and the Drow, so it is surprising to find the main Kuo Toa stronghold in the middle of a thoroughfare used by the Drow as a main route. It is also surprising to find the Kuo Toa still in business, given the seeming superior military power of the Drow, but who knows?" Anders felt that the adventures contained a great deal of imaginative material, "but while the writing style is by no means poor, the combination of florid prose and new ideas makes a text which is relatively difficult to read. Gygax does not make a regular practice of organizing his text to help the poor GM pick out the important information quickly." However, Swenson concluded that this is overall a worthwhile adventure. "The plot is interesting, and everything is well detailed. Aside from the problems I have already noted, the adventures are interesting and generally of superior quality." "