I keep a small constantly in-flux list of games that I think are both excellent and that I think are particularly valuable for game designers (specifically designers who focus on smaller, single-player indie games) to both play and seriously study. These are games that I think get a lot of things right, have solid core design principles, and importantly, are also so consistently good and so transparently good at what they do that you can just kind of study them and dig into them and find a lot of design lessons the more obsessively you pick them apart.

- Shovel Knight: is a wealth of information about solid level design, specifically about how to use and reuse mechanics in interesting ways, and how to make levels accessible using multiple mechanics/strategies. A good resource to use when thinking about how to reuse and adapt mechanics and mash genres together.

- Undertale: Games as narrative and using mechanics to reinforce narrative/philosophy. Undertale is a master-class in how to approach meaningful, artistic game design through a technical lens where you're not just saying that your game is art, you're backing that up with smart design choices that effectively communicate and reinforce your theme.

- Baba is You: Puzzle design and using systems to build puzzles, how to build puzzles that feel creative and that don't feel like busywork. Baba is You is also really hard, and there's some good lessons here about how having systems that feel playful as well as having ways to branch out and go in different directions and do different puzzles out of order can help alleviate some of the frustration that comes from really difficult puzzles -- also some of the areas where that falls slightly flat. Compare the systemic design in Baba is You and Spelunky and figure out how the design philosophies here overlap.

- Spelunky: Systemic design and how to do randomization/generation well. Spelunky does a great job of teaching the difference between breadth of content and depth of content in randomization. I think Spelunky is also a really great example of how making all of your numbers (health, inventory, etc) smaller and can make individual actions feel more impactful and can make each choice feel more meaningful. Compare with Noita, which I think goes in the opposite direction to its detriment, it's a higher-res destructible terrain that somehow feels more samey in part because of the higher granularity of destruction and stats. It is possible that Spelunky 2 should be here instead of 1, but I haven't gotten a chance to play it yet, and I've avoided spoilers so I don't know anything about it (waiting on a Linux/Non-Steam release).

- Rayman Legends: Flow state in games, level design as a communicative act with the player. When you play a lot of this game, you start to internalize how the level designers think and what motifs they use while designing levels. After a while, playing the game feels like you're just following a conversation with the level designer, you can start to predict what they're going to throw at you, and when you get into this flow state during daily challenges or endless modes, it's almost like you're dancing with the designer, you learn these "moves" and you're just endlessly executing them and trusting that the designer will act predictably. See if you can figure out how to play through the music levels where the screen gets all screwy (note that these levels are not deaf-accessible). Take a step back and think about how Rayman Legends uses consistency and repeated sections in levels to help mitigate issues like blind/unknown jumps in endless mode.

- Terraria: Terraria on its surface shouldn't be good, because it's grindy and has really broad mechanics and a ton of mini-systems that don't seem like they strictly need to be there, and the controls aren't particularly tight, and you basically need a wiki to play it well, and yet Terraria is excellent and it's worth trying to figure out why the game works so well when other games like it don't to the same degree. Terraria has a massive breadth of just... stuff. And it all kind of works because the sheer quantity of content kind of covers up the fact that you're doing random loot drops and that most of the game's systems are optional. It took me a while to start enjoying it, when I first played it I bounced off really hard. But I regularly go back to it because it breaks a lot of rules that I have and yet I still love it, so it's a good reminder that a lot of design isn't set in stone, and it's a good example of how to break design rules well. I mention that Slay the Spire below feels "generous", Terraria is also a game that feels generous: you have a bunch of rare items that are annoying to get, but there are so many of them that you're still constantly finding cool things. Pull out the systems that it has and look at how they interact with each other: most of them are optional, but many of them still have benefits or intertwine with each other in weird ways. Contrast with Starbound: why does Terraria feel like it's bursting at the seams with content vs Starbound feeling kind of samey? Revisit Spelunky and think about randomization again.