Planetfall

Reasonability:
*) computer print-out trigger -- Floyd has to be there when you read the
   computer print-out (or maybe just come into that room?) before he'll
   go into the bio-lab. The connection is not foreseeable. Since you don't
   even know that sending Floyd into the lab is the solution, how could you
   recognise the trigger?
*) Floyd's death -- This can be a long dead-end if Floyd is carrying anything
   that you need to complete the game. For example, you might send him in with
   the laser, to help him kill the mutants. He doesn't return with it.
*) finale sequence (micro-relay through end) -- You might well start this
   sequence before finishing the other tasks. There's no way to know that it
   forces you to the endgame.
*) mutant chase -- You have to know where to go, without ever having seen it.
   On the other hand, it's a reasonable place to try if you can't think of
   any good plan.

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Difficulty:
*) repairing communications -- Associating the light with the buttons. You
   get it or you don't, there's not much reasoning.
*) finding the good fromitz -- There are clues.
*) defeating microbe -- A couple of related ways, both kind of clever.

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Comments:
Quibble: Doing the flask thing 3 times is just tedious.