Also, I have updated the first post with a link to the last version.
Thank you. I played the old demo and the new release back-to-back, and the jump in quality is huge.
I do have two large complaints and one small complaint, though. The first is a bug I encountered in act 1 of Eggmansion. In the outdoors segment where the rays of light float you upwards, there is a square arrangement of spikes above the third light beam. I was playing as Knuckles, and when he hit the roof, he didn't rebound back down. He was stuck running in air, caged in by the spikes, with no way to get out or be harmed. The only way to escape was to turn on no-clip. The simplest solution would be to take away a portion of the spikes, so that if the player doesn't leave the beam of light fast enough, they don't have to be trapped forever.
The second issue I have with the game, though, is the entire last zone. It simply isn't fun to play, at least for me. It has many of the same problems I have with Eggrock Zone. There are some interesting gimmicks, such as the area with VVVVVVV style gravity switching, and the water that acts like ice, but far too much in the zone is trying to get you killed to for the player to appreciate any of it. It's hard to admire the care put into the level layouts and gimmicks when there are instant death traps around every other corner, and piles of badnicks around the remaining corners.
It's just an observation of mine, but SRB2 as a gaming platform hasn't proven itself capable of making challenging levels that are still fun to play. Part of it is the fault of certain badnicks and the numbers in which they tend to be used, part of it is the levels themselves that don't take the time to ease players into new gimmicks before those gimmicks get the players killed, and another part of it is the fault of the out-dated "one and done" continue system.
Having said this, Chemical Facility isn't quite as unforgiving as Eggrock, and I was able to complete it. Perhaps my opinion will soften as I replay the stage, but memorization off all a stage's traps should not be a prerequisite to enjoyment of the stage.
Lastly, my small complaint is another bug, this time in Eggmansion Act 2. In the darkened library area, there is a trapdoor in the bookshelf that leads to the kitchen. But if you open the trapdoor from the right side, the bookcase kills you immediately as it swings out. There is no visual indication that anything is touching you, but I'm guessing the game thinks that you are inside the door hinge and are being crushed.
Aside from my three complaints, this is a very enjoyable level pack, unquestionably among the best produced thus far. I'll also give you a hand for the amount of bizarre FiM references you managed to stick in. As a fan of that show, I got a kick out of Eggmansion Act 2 in particular.
Edit: It should be noted that my comments regarding difficulty could apply to many official Sonic games as well, both 2D and 3D. And my opinion on the difficulty of Chemical Facility Zone comes from playing through the zone as Sonic, and no other character yet.