For me, Spark Cup is all about consistency. Even Sloppy Sludge with its slippery mud, the tracks are solidly enjoyable to drive and free of jank. Most packs have some iffy maps, or at least turns/sections that can feel a bit off - but I find it hard to think of any examples for this pack.
Really, my only complaint is I wish all the maps lived up to Sweet Wonderland and Sloppy Sludge in terms of visuals.
Sloppy Sludge, despite the name, is absolutely a top 10 best map for me. The rest of the tracks, notably Sweet Wonderland and Ironbed River are easy picks when they come up in vote, too.
The only real critiscism I have is that some of the tracks really show their age. Star has improved so fast as a mapper that some of the first maps released don't quite to stack up to some of the later ones.