Many good points are made.
One thing not mentioned is the extended cruelty scale, mentioned in
ifwiki and in the documentation for rdf-intfic.
However, there are also many other points to make:
- Whether or not undo is implemented depends not only on the interpreter
and VM, but also the story itself. This is mentioned in the section of
your article about undo. (It is also possible for an interpreter to
provide "session save" and "session undo", but most interpreters do not
do this. This may also need to save auxiliary files in the session data.)
- Some games might have "sub-scenes" where you cannot save or undo within
them, and undo skips the entire scene. I don't know of any text adventure
games with this property, although it is possible.
- I disagree with the "unfairness" of Nasty/Cruel. I think that it is
good, and that a game that you cannot lose is actually an exercise in
futility, as someone had said (I forget who or where). Still, it is good
that you can have all of the kinds, and some people also might have
different preferences or just not care much about the cruelty scale.
- Randomness. Some games may involve randomness, so that what solution is
correct, and other details, can vary each time. Some games might also
re-randomize some stuff after a restore or undo, or otherwise tamper with
stuff (such as reducing your score).
- About failure and even death being a part of the story, as mentioned in
the article, you can also consider what is done in XYZABCDE.ZZT: The
medium of the computer game grants the player character the psychic power
to know that something doesn't work and to try again something else. (You
still might not know what part you did wrong, though!)
- Another possibility is if a game has multiple layers of save/restore and
undo, such as if you can undo within some system (possibly with further
effects as mentioned above), and then you can undo at the next layer to
undo the undo at the first one, which is a different layer so it is a
separate undo, and so on.
- And then, maybe there might be reasons why the cruelty rating might not
want to be seen due to a potential spoiler. I do not know of an example at
this time, but such a thing might be possible.
- In some games, even if it is always winnable, there might be stuff that
you can do, that in order to recover from it requires some more
- I think some games include the feature that you can use a command to try
to check if it is still a winnable state or not.
- Sometimes the author may have made a mistake about possibility of being
a winnable state or not, and may mistake what the cruelty rating is.