Roguelikes are a favourite genre of mine. I hesitate to use the word 'genre' because the term roguelike to me (and a lot of people) these days has gone far beyond its ASCII dungeon crawling roots, transcending general gameplay expectations and referring more to an overall design principle. A roguelike involves procedurally generated levels to some degree, permadeath (in a sense) and progressively scaling difficulty. Gameplay is built around these structure fundamentals.
I wanted to note down a few thoughts about the power of procedurally generated levels and roguelike structures in games, and how it can lend itself to well designed gameplay and push the mechanics of a game and the ability of a player to the limit.
Roguelikes (at least the ones that generate endlessly or close enough to it) naturally have an infinite skill ceiling. A well balanced and designed roguelike rewards and challenges its players in degrees depending upon the player's skill. Ideally the first level should be generally completable by anyone picking up the game for the very first time, and level 999 and beyond should still be possible yet only manageable by the utmost dedicated and focused players. Gameplay should also cater subtly to more experienced players, allowing a fast and skillful way of proceeding through these early levels.
Ideally in a roguelike (or basically any form of game), every single instance of damage directed at the player should be able to be completely avoided if the player is skillful enough, with consideration for situation. This simple design principle can encourage a game to thrive mechanically. It's what allows people to complete Dark Souls without leveling up their character at all, eventually getting to the point where nearly every attack in the game will kill them in one shot if it connects. The fact that a player is able to completely dodge every single attack directed at them theoretically allows them to take on and kill an enemy with a million health points while they only possess one, although it might take a few hours and an inhuman amount of focus. Either that or take on two dozen different enemies at once, and still have the possibility to be able to come out the other side victorious and untouched.
In a lot of games, damage avoidance boils down to not putting yourself in the situation that means the damage is directed at you at all, or knowing how to negate as much damage as possible while retaliating as effectively as possible. MOBAs and RPGs come to mind here. Other games allow you to organically read and react to threats directed at you with dodging, blocking, parrying, clever movement or otherwise negating the damage.
I find that despite the roguelike's beginnings, the structure of a roguelike game lends itself far better to the second category. Eventually in a turn-based or trade-based combat system the numbers and stats of an enemy are just going to overwhelm yours, and there is very little you can do about it except delaying the inevitable as long as possible. With an action style game however, where every attack is completely avoidable, this can help rocket the skill ceiling into the stratosphere. It allows players to push every mechanic and their own ability to the limit. A perfect player should be able to get to level 999 without being touched once, as long as they take care not to be overwhelmed or lose focus.
Aesthetically I'm also just very much attracted to an infinite game and procedural generation in general, granted the level generation algorithms are able to create consistently interesting and organic unique challenges for the player every single time. This is why I dislike predetermined room layouts or 'chunks' that are stapled together in different orders. At first it may seem like a good solution. Every room is a tailor-made challenge and it removes the risk of bland or broken organic generation. But eventually the player will see and master every layout over and over again, and after a while the game can become stale and samey. I even dislike having a mix of the two. It pulls me out of the experience if I'm exploring and come across 'the square room that has arrow traps all over the walls'. I don't mind little preset rooms for boss encounters or important treasure though.
The difficulty here comes with designing an algorithm or method that can consistently create interesting situations and engaging levels while remaining fair, balanced and possible. Simplicity and organic gameplay can help in this endeavour. I've been messing around with procedural gen and associated gameplay styles for a few years now. It's a lot of fun to play around with, although mine are relatively primitive so far and I haven't quite nailed it yet. There's a weird beauty to me in watching a generated maze grow and spiral out like the roots of a plant then going down into the boots of a little character to explore it, even in its simplest and emptiest form.
I also have a thing for the technically possible but inhumanely hard as a very optional and specialised challenge, either hidden within the game somewhere or as part of natural progression. The aforementioned Dark Souls level 1 runs fit into this category. The final ultra levels of modern arcade games such as Super Hexagon slot in here too, the utter eye-bleeding twitch-reflex stuff that comes across as a beatable challenge at the end of a long process of skill honing.
I also prefer the kind of roguelike that generates infinitely rather than having a tangible ending. It's nice to have a goal, but 'get to level 20 and bring back the Amulet of Zop' can feel a little limiting. Of course, actually completing the game is possibly going to be insanely difficult and exciting, but it's always nice to be able to go one step further, no matter how far along you are. The problem here is that high scores like;
'You reached level 6 before being poisoned to death by a giant sea urchin'
often aren't enough to keep a lot of people playing. There needs to be a balance of both gameplay and thematic progression. Some players like to feel like they're achieving or progressing toward something within the world instead of wandering in the dark until they die (which I personally like).
I guess you could do it both ways too. After retrieving the Amulet of Zop, it could have the power to take the player to a dream dimension that allows them to dungeon crawl infinitely, or just unlock an 'endless mode'. That way regular players can feel like they beat a challenge, but players interested in going further can take it as far down the rabbit-hole as they like.