I think the introduction should say more explicitly
that the PC needs motivation so that the player can
know what to do.  In this respect I think the old
Infocom games give the PC plenty of motivation.  For
instance, the opening of Enchanter describes how Krill
is gaining power and then has the Circle of Enchanters
tell the PC that only he can stop Krill.  It's easy at
that point to infer that the PC is worried about Krill
and would want to stop him.  Since to do so the PC
needs to find both Krill and the means to destroy him,
it makes sense why the PC tries to get into all areas
of Krill's castle and to pick up every spell scroll he
sees.  The difficulty with motivations is that if the
player is to have a lot of problems open to him at
once, which needs to be the case to keep the player
interested when he's stuck, then the PC has to be
motivated to solve a lot of problems at once---and
it's not easy to find sufficently broad motivations
other than finding some object or saving some person. 
(I'm not sure Planetfall and The Lurking Horror are as
undermotivated as the essay says.  In Planetfall, the
PC is marooned and sick, so he has every reason to
look everywhere in the colony for an escape and a
cure, even if the obvious actions can't be taken.  In
The Lurking Horror, once the PC sees the alchemy
professor summon a monster, the PC would reasonably
want to look everywhere for a way to stop it.  Of
course, in each of those games some puzzles may need
to be solved before the PC sees how they're related to
these broad goals or to entering an area he hasn't
searched yet.)
<P>
The idea that a game needs to make the PC's
motivations clearer as the game's goal becomes more
specific is very interesting.  Maybe that should be
more prominent, because, as the essay says, it goes
against the general rule that you should show rather
than tell when writing.  Also good is the idea that
the game needs to get easier as the PC gets more
specific motivations, since otherwise the player might
get stuck when the PC wants to do one small thing.
<P>
It's good that the essay talks about games like 9:05
and Spider and Web that trick you into thinking the PC
is motivated to do one thing rather than another.  But
praising these games seems to contradict the essay's
idea that a game should tell the player about the PC's
thoughts.  Maybe the essay could discuss more how
these two games are exceptions to this rule.  9:05
works only as a joke (though a good one) about how
adventure games work.  Spider and Web seems to work
only because (and of course this is just my
interpretation), given the futuristic setting and the
fact that the PC is a spy, it's plausible that the PC
took the precaution of giving himself false memories
right before he was captured, and so he literally
can't tell the interrogator what happened.  But it
would be annoying if a puzzle depended on the player
recognizing that the PC feels something that the
player would have no doubt about feeling if he were in
that situation---imagine how the going-to-the-bathroom
scene at the start of Leather Goddesses of Phobos
would come off if the only indication the player got
about what was going on was the first clue, "You feel
an urge."  Maybe a game in which the PC, and hence the
player, needs to pick up on his own subconscious
motivations would be interesting.
<P>