May as well go through my thoughts on the DLC courses, since I've spent the last few days playing through both those and the base courses:
Tour Paris Promenade - Aesthetically, this is a great course that really sells the Paris schtick with a strong visual identity. As far as playing on it, it's a relatively basic layout, and while the route change is neat, there's nothing much that stands out here. The course feels like it's been scaled up, and compared to the base game, the curves are all wide and the straightaways are all long. Would probably be a Shell Cup-level course if it wasn't DLC.
3DS Toad Circuit - It's a little unfair to pick on the whole Pass because of how bad the off-road textures on this one look, but it's hard to deny how crummy they are. Like, the original 3DS textures might look better. Not much to celebrate with this one, though I guess being simpler than Mario Kart Stadium makes it good for teaching remedial Mario Kart to newcomers. Feels like it's only here to make Paris Promenade look better by comparison.
N64 Choco Mountain - Decent enough remake of a very plain N64 track. The extension of the cave section is neat, the addition of a mushroom corner cut at the end is fun, and I appreciate the reuse of Bowser Castle's impacted ground to indicate where the boulders fall. Not a track I have a ton of nostalgia for, but it does what it sets out to do well enough.
Wii Coconut Mall - Yeah, the nerf to the cars is a bummer, but aside from that it's still Coconut Mall. I like the visual changes to make the colors more saturated, and while I can see where the complaints come from, it does help it fit in MK8DX a little better. I do think the use of Toad's Factory-esque conveyors belts for the elevators is a little suspicious, and it's a weird choice if they're not going to be reused for Toad's Factory.
Tour Tokyo Blur - It's a little more interesting in terms of layout than Paris Promenade, I guess, but aesthetically it just doesn't compare. As with Paris Promenade, it feels like it was scaled up too much, though maybe not to the same extent. Another course that would feel at home in either the Shell Cup or the Banana Cup if it showed up in a base game.
DS Shroom Ridge - Best traffic course currently in the game and it's not even close. Since it's a DS course, it's a little light on actual traffic, but the tight turns and narrow roadway help compensate for that. I'm hoping more traffic courses show up down the line, particularly Wii's Moonview Highway, so that this one has some competition for its crown.
GBA Sky Garden - It's fine. Compared to the other 2D courses remade for 8DX, there's not much draw to it - GBA Mario Circuit and SNES Donut Plains 3 give the player a lot of freedom in how they're tackled, to the point where the road is more of a suggestion than anything, while Cheese Land and Ribbon Road are completely reimagined with new elements, whereas SNES Rainbow Road retains its old school layout. This course doesn't do any of that, so it's just kind of here.
Tour Ninja Hideaway - Definitely the highlight of this wave. I still haven't really figured this one out, there's a ton of depth to it and a lot of unique aspects to how it works. It's a visual stunner, and unlike the Paris and Tokyo tracks, there's plenty of difficult turns and curves. Really, nothing in the rest of the game compares at all to this one.