It's also a field with a ton of material on YouTube, blogs and industry websites, so yeah, even the sources/citations in the article are only scratching the surface there. Extra Credits, Critical Gaming, Snoman Gaming, Skip the Tutorial and a fair few others are worth checking out too.
I love this topic. Care to recommend any other channels?
I prefer reading, so much more, than watching a video - plus it takes way less time, and lets me focus better.
The idea is that by the time you've finished the rest of the game, you're really good at making levels. You have a solid understanding of what makes a passage fair, balanced, engaging, and so on.
Watching pros play deathmatch in the first level is a trip.
Sometimes indies use procedural generation as a shortcut to creating levels (or replayability) without consideration for these patterns, and instead of creating an engaging varied scenario they end up being obviously disjointed and break the flow of the player.
Procedural level generation is only viable in production for games if a professional level designer can step in and tweak it.
You can think of speedrunning a puzzle game as a racing/puzzle game though :)
(He also wrote extensively about it in his blog, as I recall, though I don't have a link handy.)
They handcrafted tiles, out of which a metroidvania style levels were generated.
It consisted of a random graph generation(with constraints), and fitting the handcrafted elements to that graph.
It took the best of both worlds - a properly designed levels with tons of replayability.
Are you saying that seeing the answer is more satisfying than solving the puzzle? (as in a joke or a magic trick that you don't even try to solve?)
Think an adventure game, where in order to proceed, you have to figure out the intention of the game designer for items and combinations (and pixel hunting). Compare that to the recent zelda game, where puzzles are more free-form - where you can employ physics to solve the problem at hand (such as crossing a cravice by falling a tree trunk across it).
Many modern games are basically theme parks.
clever uses of scenery and forced perspective to give the impression of a much bigger, more detailed world than's practically possible
This is why I prefer more sandboxy games with more potential for emergence.
And in the olden days, a lot of this was basically necessary due to technical limitations. You couldn't get Breath of the Wild size worlds running on the N64 or PS1, so games like Ocarina of Time and Majora's Mask had to use careful design to make the worlds feel a lot more complex than they actually were. Same with 3D platformers like Mario 64 or Banjo-Kazooie.
No, of course not. Sometimes I want a theme park! It's just that I'm sometimes promised a world and what I get is more of a theme park. Sometimes one wants the theme park. Sometimes, one wants a more "natural" experience. This also comes in degrees, which is part of why it's tricky.
It provides a beautiful, immersive world that is ridiculous in its attention to detail. The amount of stuff to do, accurate flora and fauna, weather effects, and NPC behavior, is ridiculous.
But the moment you start a mission, things are on rails and you lose that freedom. Or the moment you commit a crime even without witnesses the law will find you like a homing pigeon. Most entities in the wild (trees, animals) are just elaborate props and there's nothing emergent about them, and random encounters are not random at all, but just selected from a pool of missions.
They're still great, but for me it did mean having to let go of the 'immersive sim' expectation and instead approach it as a ridiculously detailed version of a 'typical' GTA-style non-emergent game.
It reminds me of all those cheesy sci-fi/fantasy movies from the '70s that promised "AN ADVENTURE BEYOND YOUR WILDEST IMAGINATION".
It's a good list which can be applied side-scrollers, top-down games or even 3D games alike. The examples are great and some of those games really awaken unforgettable childhood memories. But I believe that the list could be so much longer.
Some other things which which come to my mind regarding level design: Procedural generation, Unlocking, Backtracking, Parallax effects, Mixing environments, Transforming environments, Open and Closed levels, Secrets and Cow Levels...
I'm having a great time thinking about this stuff. It's fascinating to observe those different elements while playing a game. Game mechanics are even more intricate. I think the combination of level design and game mechanics is key to creating a great game.
Game Design is not a recognized science either; a lot depends on understanding what's fun and what's not. You'll get better the longer you play around.
What distinguishes a good game designer from a beginner is years of practice. To achieve that, you have to be able to try new things in a very short time. Learn a game engine, which is widespread and does a lot of work for you (create games and not a game engine). Unity or Godot for example. Start small. Games you can finish within 1-2 weeks. If you can do that, you can write dozens of small games a year. You get faster and maybe find your own style. Here's a great resources which shows you, how someone from the indie community can approach it:  
Something I can't recommend enough are Game Jams. Take a look at Ludum Dare . It really is fun to think up and implement a concept within a short time. And you learn a lot, through the process itself, through the feedback of the wonderful community and by playing other games. The next jam starts on October 4th.
I've been going through Unity but it's been a lot harder than I thought. I'm hoping to get to a point where I can participate in a game jam soon.
I always found that some of the platformer games of consoles, like Super Mario, Donkey Kong, had much more simplistic and kind of boring levels. You did not had to collect keys to enter doors, or do other more complicated things, but basically it was mostly dexterity.
This aspect comes a bit short in this article, I think. To me it was always kind of crucial, how much such puzzle element there was in the game, whether I liked a platformer game or not.