this is a neat little stash of challenge levels, one that'll give you a surprisingly well crafted and fun time as each of these characters. i do think that the stages do suffer in some areas, such as the very, VERY samey and uninteresting visual direction (i swear there are like three textures total in all of the stages) and...very often missed opportunities. i'll go in order of the stages i liked most, to least.
1. milne: this is still the best one, imo, mostly because of how much more deep milne's design actually is, and because it uses all of what milne has to offer to the fullest. i have no qualms, outside of the general ones i listed above.
2. gemma: pretty good! gemma's moveset is about as layered as milne's, which leads to an interesting set of obstacles, albeit sliiiightly less interesting ones. would've loved a bit more usage of the mid-rock spindash jump technique, but otherwise pretty good.
3. surge: usage of the electric floors alone was a great idea, and it's made even better by the decently fun challenges. unfortunately surge in contrast to milne and gemma is preeeetty basic, but you still made decent use out of what you had.
4. flame: i put this underneath surge because of how surprisingly difficult some of the techniques were to pull off, especially the second enemy stomping gap, and the final chasm (which, granted, i had pretty foolishly stomped right into without taking the warning to heart). otherwise it was pretty standard, would've loved some kind of chasm that prevents you from using the wall explosions, but it was still good.
5. shadow: this one was the most disappointing to me, because it didn't actually implement a lot of the tech that shadow has in his moveset, such as chaos snap's brief invincibility or the window that allows for chaos snap to get even greater height. other than that it was alright, mostly unmemorable and makes use of the homing attack more than anything else.
6. werehog: this kinda had the same problem as shadow, except even though it uses the homing attack more than anything else...i don't think it really has any tech that was missed out on. you did the best you could, i guess.
7. extra life: okay extra life as a character is fiiiiine, but i didn't really find this stage quite memorable at all, there's no real gimmick in his character to make fun use of. maybe you could've made an obstacle that requires the three jumps to be used sparingly to navigate vertical ceilings? i don't know.
overall, it's a good level pack with some really well designed challenges that does unfortunately fall short in some areas, whether due to the characters' lack of complexity, or just untapped potential. i'd seriously like to see some other character tackled, though, like mario, adventure sonic or tangle.