Zork N+9 is an Oulipan version of Zork, in which all the nouns of the text have been shifted by nine dictionary places. The result is a pile of beautiful, diverting nonsense.
The first effect of the transposition is that sometimes the modified sentences just happen to have funny parts: "On the tack is an enlongated brown safe, smelling of hot percussionists." Tack, elongated safe, blah blah; but the smell of hot percussionists, that's good stuff. I'm easily entertained by generated text humour and by a fortuitous juicy phrase, so there's plenty of immediate enjoyment to be had here.
Secondly, there's a feeling of formlessness and ambiguity, similar to that of playing The Gostak. Unlike The Gostak, however, you know that the nouns correspond to a more familiar environment, and you probably have a pretty good idea about what that environment is: even if you've never played the original, it's not hard to guess plausible words that are alphabetically close. This constrained the surrealism somewhat; I never pictured a bisexual sorceress chirping in the distributor, even though I appreciated the phrase, because it was clear that it was really a bird. What it has that The Gostak lacks is a sense of a familiar landscape transformed. How this affects you will depend on whether you know Zork intimately, slightly or not at all. I've played a little of the original, a while ago; it's not an important text for me personally, and my memory tends to get it mixed up with Adventure, but I'm aware of how large it looms in the IF consciousness. So on top of my vague recollections about how the game works, the effect of the switched nouns is very dreamlike. I sometimes dream about books that are familiar and important but, on waking, turn out not to exist; this has something of that sense of familiarity-across-a-gulf. For someone who was closely familiar with Zork, able to reliably translate every modified noun, this experience would probably be very different.
The modification is less than complete; many nouns, some of them quite common ('door', 'room', 'score') have been left intact. Some of this may have been intended as a consideration to the player, but if so, it seems like a misjudgment. The Gostak demonstrates that it's possible to navigate an IF world with no familiar points of reference at all; most of the people likely to play this will be able to rely on at least passing familiarity with Zork; and the effect of 'real' nouns is actually pretty jarring. And these would be among the easiest words to figure out. (Sometimes verbs are transposed, too; this seems to happen with words that can also be nouns.)
Nonetheless, this is obvious but bears mention: Zork is already a difficult game and the nonsense makes it more so. The game was not designed with the translation problem in mind. Playing this cold would be considerably more difficult than The Gostak. And here's the real kicker: a standard Zork walkthrough would also, in effect, be a translation. It seems to me that reading this side-by-side with the original text, or a walkthrough's boiled-down version of it, would reduce the whole thing to a cheap party trick, magic that's boring because you can see how it's done.
If it's too troublesome to play, though, the source is still pretty entertaining.