There were a few good levels, such as Sakura Solstice, Panic's Fury, and NEW Pipe Towers Zone, and there were alotta mediocre levels. I beat every singleplayer level as Sonic with no mods, without going super, and without using the console command that makes everything easier. However, I didn't try any of the multiplayer-only levels.
There notably was an outstandingly bad singleplayer level in this level pack; Personalized Palace, which for whichever reason is referred to in this mod's overview as Forest Palace.
Now, from a technical standpoint, Personalized Palace was impressive, and from a thematic standpoint(including its visuals), it was generally enjoyable, but concerning its other level design, it was awful.
It had a number of bad level design decisions, such as:
-paintings you had to jump through that led to you immediately getting hurt or falling into a pit that put you back at the start of the level just because you weren't an IRL psychic who knew what was on the other side before the 1st time you tried out the level(e.g., the cloud section, the city section, & the well section if you moved the wrong way and pulled a deton while initially falling in)
-Detons being placed smack dab next to vital objects such as underwater springs and stars that you need to collect in order to beat the level
-Crawla Commander spam that results in the player just spindashing in place until their eyes all turn yellow and then just running past them all because they're often too fast to simply ignore them and keep moving until you've done that
-a complete lack of starposts, though that in particular can be forgiven because of how the stars are tracked
-the level takes over 20 minutes to beat at a faster-than-casual pace; this by itself wouldn't be bad if not for the level's other issues, however
The level would've been enjoyable overall if you didn't have to get every single star that could be found without extensive digging around, plus a few more stars, before the goalpost would be revealed to the player; only needing, say, 8 stars would've made the level be just fine.
On another note, I will admit that I am guilty of bad level design myself, but I've gotten better at it over time, and I'm sure Bandder will too, so don't take it too hard.
Personalized Palace alone lowered my overall rating by 1 star, from "Good" to "Okay" in part because it took me a bit longer to beat this single level than it took me to beat all of the other singleplayer levels combined, which sort of means that it constitutes more than half of the singleplayer level pack all by itself.