[sblom]

A game like Rogue.

Slightly less obtusely, it usually was a procedurally generated dungeon-crawler with potions and scrolls and varied weapons to use against varied mobs. When you died, you were dead. Your character began each time with no knowledge and had to learn what a "cloudy red potion" happens to be this time around by drinking it or using an identify scroll.

[Kluggy]

So the change is that players knowledge keeps in “modern” versions and in classic versions, your memory was largely useless?

[mcphage]

The biggest difference (as I understand it), is that in classical roguelikes, nothing persisted from run to run. In modern ones, you build your character up over a sequence of runs, so that in later games you're more powerful and can go further. But in classic roguelikes, every run is like the first. So a player's knowledge is the only thing that does keep—they learn the game better, learn the systems better, and progress further because of that. Not because of anything they unlocked in-game over a series of runs.