I picked this up on whim the other day at a used book store for $3. It was loose (out of the box), and included the Quest Book, the Rules Book, the DM Screen, some character sheets and a monster list, and 11 double-sided, perforated dungeon layout sheets, with a 1" grid. It has a TSR and a Blizzard logo on the front, and the copyright is 1999, TSR, with TSR being a subsidiary of Wizards of the Coast. The stats are all 2e, though the character sheets list it as "To-Hit: 19" rather than "THAC0: 19".
I haven't really looked through it that much, except just now to type this post. I never played Diablo, though all my friends did, and I mainly picked it up because it was $3 and I thought the dungeon tiles might come in handy some day. I also got a Dungeoneer's Survival Guide for $8, and that's pretty much my favorite 1e book. (If I were going to run a underdark campaign for any edition of D&D, the DSG would be my bible.)