Keef the Thief was one the first games I ever bought from a computer shop, it was in the bargain bin for $50 (quite a lot of money back then) because the code sheet to enter the game was missing, so I had to guess the answer to the copy protection every time I wanted to play, consequently once I had it running I would play for days so I didn't have to guess again.
I was immediately hooked by the humour used in the game, which was allegedly just meant to be filler text to be replaced later, but whoever was in charge liked it so it stayed.
I loved disarming (or not) the traps and the combat system whilst quite strange, was actually pretty good considering what other games were doing at the time.
The amount of times I got endlessly lost in the map, till I memorised it.
I particularly liked that once you won the game you were allowed to keep playing if you wanted.
Not only do I think this should be on GOG, I think this game is dying for a remake or even a sequel, though I think the comedy aspect should not be left out, I think it made the game.