I too am psyched for this. Procedural content always reminds me of like improvisational jazz.
They're both perpetually unique.
Yet they both run the risk of feeling forever the same.
The way Casey put it (I think), roughly, 'things made by algorithm tend to look like they were made by an algorithm.'
So you run into the problem of having an infinite minecraft world, but little reason to leave your spawn, since it's all the same every way you go (they've addressed this a bit, but last time I played those solutions still felt a bit like band-aids on a cracked foundation).
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The second big pitfall I usually think of re procedural content is the risk that players will feel they need to keep playing for some certain output from the RNG gods...
This was an epiphany I had playing FTL: At some point (regrettably, I had to cave and look up how to unlock those last few ships) I found myself replaying the game over and over hoping to get the right combination of systems and random events to unlock those last couple ships (a new ship, after all, is new content.. one of the biggest rewards you can offer a player..) and I recognized an important and sharp distinction between the feeling of "
playing more to get better" and "
playing more to obtain a certain random output."
Personally, when I find myself in the category of the latter, I know it's time to quit that game: I've gotten everything out of it I will. At that point, it's just a glorified slot machine.
This maybe isn't so much related to the procedural content as much as the way the systems around that content function... but I thought I'd mention it. Also it's just my own personal preference when it comes to games (after all, some people really enjoy slot machines!).
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In case anyone hasn't seen it, check out
this for a neat interactive explanation of Spelunky's random level generation. I thought Derek Yu had an article on this himself, but
this was the closest thing I could find, maybe it's what I had in mind. He mentions briefly how it works.