There are certainly similarities in prose between Zork and A Connecticut Yankee, mainly in their snarky disdain for what they regard as idiocy ("A jackass is valuable to this world because he is a jackass; but a nobleman is not valuable because he is a jackass." and "Don't you believe me? The mountains are impassable!") One can almost invision the face of the narrator of Zork, trying not to laugh at your obvious incompetence, and the face of Hank as he listens to Sandy's horrible rants, and they would be the same face.
Or perhaps that's just the face of my narrator, and everyone else is doing swimmingly. I do not believe I am very good at text based adventure games.
They are both linear narratives in the sense that they have a definite beginning and conclusion that do not change with time. And even though Zork presents you with choices to make, it is essentialy a binary tale that ends one of two ways, either you die horribly or win. (We'll not count getting frustrated and giving up here, because that's just counter-productive) In the same sense you either finish reading A Connecticut Yankee or you don't. Both are fantastic tales, if not in quality then in nature.
Where they differ most obviously to me is the amount of effort it requires of the reader/user to get to a winning end condition. Where Twain lays the story out for you to follow, and reading it is a pleasure for those who take the English language as a form of art, Zork forces you to interact with a dumb agent who may or may not reward you with some pithy text if you guess the right string of words to type. Is it useful to compare the two merely as stories then? By this measure I'm afraid Zork falls flat. It is certainly cleverly executed, but the idea of wandering about collecting treasure and living in constant fear of the Grue is simply not as compelling as the tale of Hank and his misadventures attempting to civilize medieval Britain.
And yet there is one more way in which both may be considered kindred. Both were largely experimental and responsible for minor revolutions in their genre, to varying degrees. This is really about it, though. Zork was made not just to tell a story, but to do it in a new and unique way, for which it deserves credit. It does not, however, deserve to be classed with Mark Twain as a work of literature or fiction. Here is where the usefulness of comparing the two runs out.