I thought there were only the two:
Tower of Doom
Shadow over Mystara
So this "one of the three Mystara games" confuses me...
I owned Shadow over Mystara for a bit... it wasn't that fun in a home setting, when it was usually just me playing it.
I got really good at the opening parts of the game, but rarely played long enough to get deeper, into the further paths/parts of the game, just because it takes so long to get there.