This is my review of the single-player levels:
Jade Hill Zone, Act 1: 5/10
There isn't much wrong with this one, but it isn't a winner and it just isn't very entertaining. It's generally lacking in gameplay and gimmicks all over, and needs a bit more to explore. The scenery and length were nice.
Jade Hill Zone, Act 2: 3/10
At first, it was just as the first. However, as I went on, the level dragged on forever. There's ridiculous challenges involving jumping from small pillars to another at high heights, a large amount of wide and open areas with nothing to do, and it's very ugly and isn't a pleasant sight.
Remove the pillar-jumping challenges with something else, fill up the giant square hallways with some detail, objects, and gimmicks, so they don't seem so dreadfully boring and long.
Jade Hill Zone, Act 3: 5/10
It's nothing more than a round room with Eggman in it. It's too large and the boss is ridiculously easy, even without Rings. He's easily fooled into staying in a corner and doing nothing. Find a way to make fighting Eggman interesting.
Toxic Plant Zone, Act 1: 3/10
The level's difficulty isn't fair at the start for most beginners. People new to the game won't know how to cross such large jumps.
There's an instant-death laser, which should be flashing (I'm sure there's a Linedef Action that does this), and give only non-elemental damage.
The whole level is mostly a large amount of big rooms with nothing filling them up, or bland walkways. Fill those rooms up and add detail.
Toxic Plant Zone, Act 2: 2/10
Extremely easy. It's walking for the most part, with little jumps or challenges to find. The rooms are mostly far too large and feel extremely empty and boring. There isn't much texture variation, either.
Toxic Plant Zone, Act 3: 3/10
Another unoriginal boss. It's actually very easy, and the giant pit can be ignored if you're skilled enough.
Hidden Forest Zone, Act 1: 2/10
This level is very unfair. Not only does it contain several unfair traps, it also features puzzles which make almost no sense, frustrating the player. Remove the puzzles where you walk through walls and floors. They simply don't make much sense and you didn't give the player a sign as to what they're meant to do.
There's this one area where there's a giant river with branches. For whatever reason, the floor kills you instantly, which you wouldn't expect. This room goes on for a very long time, and it has extremely small platforms which are spread very far apart. After this is another wide, open room, where you have to get on a branch.
You then talk a long walk to a bunch of pillars, which are unfairly spaced, and are over a death pit. After this is another series of pillars, except you have to use a Spring to make it to one in the center of a circle.
Remove the puzzle aspects of this level, get rid of the death pit area, and replace them with something else. This level has some detail, but it's severely lacking.
Hidden Forest Zone, Act 2: 2/10
More of the same. It contains several unfair challenges and traps, and it's very wide and open.
Hidden Forest Act 3: 1/10
This boss is very easy. You're meant to guide the turrets' fire into Eggman. Mostly, what you have to do is run in circles while the boss nearly plays itself. It takes far too long to complete, and it's very ugly.
Overall:
Overall, this mod is a pretty bad one. While it DID show some promise in the first Act, it all seemed to go away significantly, becoming frustrating, boring, and a chore to play. The rooms are generally ugly, unfair, and boring.
3/10