I see that Eye of the Beholder and Dungeon Master are noted as the inspiration for Grimrock, but for me it seem much more like a Lands of Lore inspired which is perfect in my mind. I am a devoted old school RPGer and games like this (and Wasteland 2 and Banner Saga) make me very happy indeed.
So what your fave old school grid dungeon crawler. Lands of Lore is king in my book, but EOB 1 and 2 are also great.
Heres my classic old school/big box + other RPG shelf. I do have a habit of posting this pic whenever I can.
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As you can see no Dungeon Master, but I do own Stonekeep on GOG (lost that box years ago).