Boomerang Cup done now as well. Bangkok and Singapore much superior to Amsterdam, and Singapore for me is the best city track. Vibrant, fun, and involved with some nice mechanics (enjoyed the neon speed trips).
Waluigi Stadium I think works nicely, though I found the music remix to be too... jolly for a mud bath Waluigi course? Felt a little jarring. Would've appreciated more mud splashes, too, given how shiny and wet the course looks. I like the addition of the higher, anti-grav sections above the track. I'd say the number of alternate routes is a strength in the city tracks and the stadium in this Cup.
Mario Circuit DS is another one I have a soft spot for. I unapologetically take a lot of enjoyment out playing in a vanilla race track in the Mario Universe. One thing I really liked here is the lighting: there's a lot of depth and subtlety to it and it makes the course more interesting visually. A huge improvement over the flat lighting in wave 1, which makes Toad Circuit especially kinda washed out.
However, there is now a deeply troubling implication that arises from Mario Circuit DS, Peach Gardens, and Royal Raceway being present in the same game. Indeed, I am now deeply concerned about the governance of the Mushroom Kingdom. Peach appears to have forced her subjects to build two, enormous and identical castles, and this is in addition to her enormous country estate (Peach Gardens). There's also the alarming possibility that there is in fact only one Peach's Castle, and that Peach forces her subjects to rebuild whichever course she wants to race on around the castle, which is surely a resource and labour intensive process. I do hope the international community condemn the excesses of the Mushroom Kingdom's monarch, because there are some troubling signs.