Eclosion

1) The puzzle is neither too easy nor too hard. You can beat the game in several minutes - but it gives you a surprising amount of satisfaction for such a short playtime.

2) The sequence puzzle perfectly fits the choice-based format. When all the options are laid out openly in front of the player and they don't have to guess the right actions - how can you make the player think, create the element of surprise? By making them guess the right sequence of the given actions, of course.

3) The choice-based format perfectly fits the xenobiology puzzle. Imagine if you had to type commands you need here - like DISENGAGE CREMASTRAL HOOK - again and again in a parser game; Twine mercifully lets us just click the links.

4) The game gives you interesting feedback when you do things in a wrong order. There are 7 different ways to kill a pharate; there are 94 losing paths through every game cycle and only one way to win. But when your plan goes south, you always learn something new and put together a new plan in the light of fresh information.

5) The game's horrific nature is not just for the sake of horror. It suits another purpose: the creatures are so monstrous, evil and repulsive that the player isn't likely to feel sympathy and get attached; so they can experiment freely and sacrifice as many pharates as they like while trying to understand the logic of the puzzle.

6) It's well-written. Laconic phrases and preteritions let the player's imagination run wild; that's one of the strengths of interactive fiction, an effect which is hard to achieve in a graphic game.