I like that in general: just having a little bit of unpredictability in each level. And I really like dense level design with a lot going on. I think… - Derek Yu

Everything in Spelunky was designed with a similar sensibility, where we're trying to draw out the personality of each area, of each monster, from very simple actions and things that they do. And when they all come together, you get this complexity that's very interesting, and that makes every time you play in this randomized environment fun— because you start to see — over time — all the different patterns that can arise. [...] That's the emergent gameplay that comes out of it.

One of the most fun things about games is learning. It's learning the game and getting that knowledge for yourself about this little world. The only way you can really do that is by figuring it out yourself. If the game tells me something before I get a chance to learn it myself: 1) that's really annoying, but 2) it robs [me] of that experience.

Miyamoto and Tezuka, at least when they were designing the early Mario games— I've seen interviews where they describe the genre that Mario is in — and that they're working in — not as platformers but as "athletic games". [...] When I read that, that really changed the way I saw these games— and I feel like it captures the spirit of them much better than "platformer". Even the platformers that Mario has inspired afterwards don't feel as much like "athletic games" [as] the Mario series itself. And one of the iconic Mario songs by Koji Kondo is called "Athletic Theme", which plays into that.