Valve used to do fun stuff before they turned into a full-time storefront. I was hoping a new ARG would happen in the days up to another announcement of a new game like they did with Potato Sack/Portal 2. However, HL:Alyx was announced without anything leading up to it. Now it's actually becoming difficult to even find a record of the Potato Sack ARG even happening. Most related websites and wikis are gone now. Even the GlaDOS@Home finale wasn't preserved at all. Describing it after the fact doesn't really begin to come close in detailing just how massive the whole event was.
The Potato Sack ARG, for all of its flaws, almost managed to become bigger than the game it was based around... I never saw nearly as much activity or interaction from the community since that time. Seems a shame that something this intricate and involved could only happen once.
It was estimated about 1,800 people managed to get all 36 potatoes. The prize, for a time, was... having 36 potatoes on your Steam profile page.
Later, those who got 36 potatoes were awarded every game in Valve's Complete Pack, plus the newest: Portal 2. I ended up figuring out, a little while after the fact, why there were 36 potatoes: That's how many games were in the Valve Complete Pack once you included Portal 2. This clue was never discovered during the ARG so nobody knew until the ARG was over whether or not there was going to be a prize for gathering all 36 potatoes.
This was one of those times where just seeing it through was enough of a prize in of itself. Hope to see something like it again in the future.