From time to time I'll get the urge to play some "interactive fiction" - known back in the day as text adventures, with the big names being Infocom and (in the UK) Magnetic Scrolls. I recently had that feeling. Reading up on a bunch of old ZX Spectrum computer games, I wanted to play something from that era. Level 9 had a reputation as a major publisher during that period, so I thought I'd try one of theirs.
I thought I'd try the classic Gnome Ranger. I fired it up, explored for a little bit, quite enjoying the start, and then got solidly stuck. I got the sense that this wasn't for me, and wasn't heavily invested in it, so rather than persevere I took a look at a walkthrough. The given solution left me glad that hadn't tried to put the effort in to find it.
This lead me to thinking about what I like in text adventures, and what doesn't work for me, since the difference seems incredibly stark.
I think the key concept is that a text adventure needs to be "goal-oriented": There's something you're trying to achieve, and the actions you take should be relevant to achieving that goal. At the simplest level, games like Advent and The Guild of Thieves have you collecting treasure: a simple, obvious goal. Others, like Christminster, Trinity and Jinxster (all of which I highly rate) have some kind of higher goal, and your efforts are directed by that. Both The Pawn and Gnome Ranger seem to dump you in a landscape to wander around, trying unmotivated things until something happens.
The critically-acclaimed game Curses is also a little of the "wander around, trying things" persuasion, but it demonstrates another aspect Gnome Ranger lacks: a structure to help you understand if you're on-track. In Curses, you might come across an interesting situation, play around with it, and get the gist of whether you're attempting what was intended, and whether it's helpful. Gnome Ranger leaves you wondering, trying all the actions you can think of to provoke some reaction, rather than progress logically.
The third thing that made Gnome Ranger not for me were the non-player characters (NPCs). Pretending there are other sentient beings in a game is tough, doing it right is hard, and the illusion is easily broken. So, nobody really does it right. In practice, NPCs are automata that you can get information from, that you can do things to, or can do things to you. Their purpose is highly ambiguous; whereas it's pretty clear what a lamp is for, what are you supposed to do with a nymph? Oh, and they have an annoying habit of wandering off, because aimless wandering is apparently realism.
Inevitably, though, in an NPC-heavy game, you'll end up treating NPCs as your personal robots. There'll be some command of the form "walrus, n, n, pull lever, e, get gem, w, s, s, give gem to me", which I feel is both a soul-less puzzle and an excellent way to break any suspension of disbelief you might have managed. In short, NPC-heavy games leave me cold: they weaken the focus, weaken the atmosphere, and encourage lazy puzzles.
NPCs aren't inherently a disaster, they just need to be carefully managed. Non-sentient, or at least non-verbal NPCs can have a clear purpose, and avoid the complexities of following commands or answering questions. A magpie that steals shiny things can form the basis for a puzzle with no complications. Well-defined roles can also constrain expectations and signal plot. Bar staff or ticket inspectors, focused on their job and nothing more, can work well. Open-endedness is a problem.
So, there we go, we now have Simon's three rules for building good interactive fiction: Ensure the player is motivated by an overall goal, provide logical puzzles that give clear feedback along the way, and ensure your NPCs are well-defined.