"All 96 courses" in Mario Kart 8 Deluxe.
Sure, Nintendo has the time and talent to make as many courses as they want nowadays, but for one Mario Kart game, that's pretty impressive. And while I still think the Wii U was Nintendo's best console and have never truly felt at home with the Switch, it's clearly the success of the Switch that prompted the "deluxe" port and the wide expansion.
On either console, the game's simple-to-use online mode is its functional triumph, letting 12 people from across the world compete on any of the courses with some kind of approximation-based implementation that defines away lag and almost never gives up the connection; something that's been present since Mario Kart 7 on the original DS. What a profound feeling, from the first time and ever after.
The selection of courses? Emphasis on variety, which I guess is an attempt to please everyone, but must mean many await disappointment at the randomness- or vote-based online course selection each round as their next not-so-favourite course is chosen again. Nintendo will almost never just do the same conceptual game twice, so Mario Kart 8 has inherited many sometimes literally groundbreaking mechanics: karts and bikes, tilt and wheel controls, flipping from half-pipes like a skateboarder, and anti-grav sections of track that shed the notion of "up." So some courses are overly flighty, and it's not always as fun as it sounds. On the other hand, a range of courses from "Mario Kart Tour" also made it in, largely calm and flat, but based on real-world cities rather than the more colourful and comforting locales of Mario's world. Tour was made for the accelerometer controls of other companies' handheld devices as something of a gateway… appetizer, and its courses also have a habit of reusing different pathways amid the same terrain with forced detours to create three varied "laps."
But the courses that really speak to my heart are the returning originals from Super Mario Kart and Mario Kart 64. The original games, despite the infant and adolescent graphics, had places my imagination treated as real, and the handful adopted into Mario Kart 8 were so carefully redone as to feel like invitations to return to these places with almost no imaginary aid. And drive around. The grip of the flat pavement from Mario Circuit 3 with the clear, colourful barrier blocks, or the dirt and puddles of Donut Plains. Three laps, with rhythm and routine, the feeling of taking the curve, noting what was off, and refining it next lap. That remains this game's aesthetic and spiritual triumph – as well as, importantly, the retained ability to play as yourself, thanks to Miis. I wish they'd just done as Mario Kart: Super Circuit did and secretly resurrected the entire first game's locations.