I found this a couple of years ago on Amazon and thought it was so cool that we bought it. We've enjoyed looking at the components and the rule book and the Book of Worlds, but we haven't played it. Honestly, we haven't played much in the last 10 years or so. Our kids really cramped our style. (Yes, we wanted to raise gaming kids, but that didn't really work our so well.)
When I saw they were actually going to play, I looked at BGG more carefully and got out 504 and fiddled with the pieces. Something that I found that's really cool is "A rule Summary Sheet Generator" by Nick Johnson (Arachnid). It takes the three section summaries that you find in the Book of Worlds and combines the three pieces in a more useful order. For example, the components you need would be listed in three different places in the book, but are all listed at the top at https://504rules.github.io/. It's an impressive piece of work, but not as impressive as the game.
Of course, I want to play them all, but that's going to take awhile. Especially considering we haven't even started yet.
August 4, 2019