By any reasonable standard of craft, Cheiron is a very poorly-made piece. It was not originally designed for general consumption, and only marginally as a game. Rather, it was designed by med students as a study tool. It's technically fiction, but it's the fiction of training scenarios, intentionally avoiding literary qualities.
The game contains four patients. You need to diagnose them using the standard methods available to a doctor: part of this lies in asking them about a fixed set of topics, and part of it involves a physical examination using a lot of specialist verbs (AUSCULTATE) and an immense list of anatomical nouns (FIFTH CRANIAL NERVE, STANDING BLOOD PRESSURE). Some of this is accompanied by stock medical photographs. The overwhelming majority of details are default responses, some of them totally inappropriate. All the patients are built from the same template and imperfectly customised, so you can (for instance) receive assurances from male patients that they are menstruating normally.
Given the game's intent as a revision tool and its sandboxy implementation, it's easy to assume that the patients will have a different condition each time. This was, I think, the original design intent, but it was never accomplished. Worse, once you've reached a diagnosis there's no way to tell the game this; the answers are included, and you have to be satisfied with that.
All this said, I had a hugely entertaining time with Cheiron. I played together with an EMT and anatomy student, and we made heavy use of internet resources. Divorced from its usual context -- the anxiety that you or someone you care about might have some horrible condition -- amateur diagnosis becomes a fascinating mystery, a complicated puzzle striking a balance between research, deduction and informed guesswork that I haven't seen equaled in any IF mystery. Most IF is designed to be self-contained, requiring as little external knowledge as possible; Cheiron demonstrates that taking the opposite approach can be compelling, although it doesn't suggest that it could be done in a stable and easily-played way.
The answers are telegraphed slightly -- you can't send off for lab tests, but you can see the results of the tests that a qualified doctor sent off for. The choice of tests alone is often a strong clue, but it still requires some interpretation.
Cheiron could, with a vast investment of work, have been turned into an excellent game. As it stands, its half-baked implementation will probably make it a frustrating experience for most players, its heavy requirement of specialist knowledge is likely to seem unfair, and some will find its focus on disease and infirmity off-putting.