There's a line I've found myself saying a lot lately: Writing an ARG is to writing a novel what performing on Broadway is to performing for cinema. Performance art, where the audience reaction matters. An active art, not a passive one.
But it's even a step beyond that. Writing for an ARG is a little bit like being a live performer, where every night is opening night. This means every line you put out there is untested - are the plot points close enough together to be connected, while still not being too predictable? Are the jokes funny? Are the characters sympathetic? Are the challenges too easy, or too hard?
There's not a lot of opportunity to adjust on the fly based on audience reaction, either - once you're put a piece of information out there, you can't take it back. And it can be very difficult to gauge the abilities and expectations of your audience, with potentially disastrous results when you get it wrong. Groups of puppetmasters have had experiences on both ends of that spectrum: either the audience voraciously tears through everything in record time; or else the 'perfectly obvious' clue goes unsolved, or worse, unnoticed. This just shows that there's a narrow path to walk down, and it's pretty easy to stumble.
There are advantages to having every night be opening night, too. You never get tired of your own material, because you're not throwing out the same overly calculated elements week after week. There's always a certain freshness to your work. And just like in performance theater, there's a visceral thrill to the interaction.
In fact, I've become so used to nearly instant feedback in writing that now that I'm working on a number of projects that won't see an audience for months or years (including that mythical novel of mine)... I find I'm a little lonesome. I'm spoiled, and entirely unsure how to write in a vacuum anymore.