Okay here is what I gathered so far. Keep in mind we are thinking of first time below average player using Sonic :
ACT 1
I played through the left path, so I don't know much about the right path (yet).
_ Left path 1rst room : Snail shooting in a crushing/pit falling room. Too much.
_ Left path : I suggest the first introduction of the blue spiked badnik not being so much near the upside down convoyor belt room. Or at least place the Armageddon shield next to it because it is not visible enough.
_ Left path lava room : Snail imparing your platforming even when you DO reach the air uplifting green platform (not instant death unless you have no ring)
ACT 2
I played through the right path for now. (after the first checkpoint)
_ Auto bullet shooting room with snails and death pits. You have to slow down but at the same time you have to speed up. That's the feeling I got while playing here the first times.
_ I replayed the blue plaftorm room : the upper square blue platform has a death pit hole from behind/on it, and you CAN'T see it from the get go. (stupid death)
_ Further : a white conveyor belt with a crusher, two death pits, and an annoying snail + 2 red moving up and down lasers. The conveyor belt and snails force you to react fast, while the lasers force you to slow down (the first times) because of the death pit threat.
_You already know about the Megaman blocks room. The snail aside people will still die here... It can't be improved much more than removing the snail.
_Near the end of Act 2 there's many gimmick one after the others. They are balanced by the fact that they're not simultaneous, but the conveyor belt leads to a bottom less pit where 3 red lasers are moving up and down. It is too much at once just after those crushing gimmicks just before.
The outerspace sections were improved so I guess they don't need any further tweeking. I still have the strange feeling it will frustate someone, but I don't feel it anymore myself.
It's been years since I tried right path in Act 1 and left path in Act 2 and actually progressing. I will have to see them too.
ACT 3
In my opinion the worst. But in the strangest ways possible. Keep also in mind that the final timer is also a dying gimmick (which you must try to prevent).
_Second room : there does not need conveyor belts to serve as platfom as you are jumping to stay ahead of Metal Sonic. It is not hard when you memorized it (dying) or slow down... but you are racing.
_The first red lasers are okay because they are placed in a way that there are not hard to not touch but their placement near death pit is disrupting when you are just going fast. Many people will feel forced to slow down or get hit. Even if getting hit does not make you fall (thanksfully). Slowing down is inevitable.
_I don't get the platforming room where you have to climb 3 platforms to turn before Metal Sonic arrive and make a hole in the spikes. Is it actually trying to slow you down when you are ahead ? Letting Metal Sonic make a hole sound more seducing and effective. Plain Bad room.
_The 2 slow large red lasers... Should be much less large, you will run into them too easily. Slow down again, or get hit.
_The white conveyor belt room with 3 red lasers moving up and down. You won't believe just how many time you can actually be touched by them if you try to jump over them, or just run mindlessly. It just forces you to slow down.
_The reverse square platform room, above bottomless pit is not playable at full speed (new player remember). It is easy if you slow down, but again, this is a race.
_A reverse gravity hallway of spikes ? Like a jumping obstacle course where you have to jump over multiples lines of spike while running/thoking perfectly one after the other ? Really, it would be a fine room if it wasn't a race.
The 3rd act is unbelivable. I laugh so hard when I see. It is so well balanced to the point where it is bland in itself, if Metal Sonic doesn't exist. Clean, linear, easy, you say it. But at the same time it is so well designed to make you lose on purpose it doesn't even try to hide it. Considering that Metal Sonic arriving at the goal before you is a defeat (death) everything in here becomes hell, because everything is build around pure memorisation. If you play slowly without ever trying to win, you WILL learn the layout of this level, and after forgiving to Metal Sonic many lives (that not everyone will have by the way), you can outspeed him and beat him to the race.
It is shamefully, laughably alien. ERZ Act 3 is like the exact reverse of the difficulty of the entire ERZ previously, while still making it next to impossible to not die.
Incredible. I am in awe before such craziness it's like I see in the 4th dimension.
The level is actually damn fine layout-wise, while being very mean in practice.
Act 3 will catch off gard pretty much everyone. Everyone except for players that are used to the process of speedrunning and don't mind losing the first times.
Did I mentioned how pretty the Game Over screen is ? And how loved and lovable you feel when you see once again you save at Egg Rock, after losing dozens of lives (if you had so many) in ERZ Act 3 ?
Act 3 is the black sheep. It will punish the players who try the hardest to not lose, without understanding its process of Trial and error. Trial and Error punished by death, and return back to Act 1.
Act 3 is so alien, I actually now think the only thing it does really need is the game saving just right there as if it was a new zone. If you do that, it will be the equivalent of having infinite lives, and the Act will be truly playable.
Granted it is a stupid Try and Die level in it's entirety because of the race, but it his main flaw. I would also suggest making the 5th room (where Metal Sonic breaks a blocking line of spikes) not encouraging for the player to just let Metal Sonic outrun you, even when you painfully managed to outrun him before hand.
Act 3 is hard in a ridiculous way : it is the very proof ERZ is nothing more than die and memorize. Awful in an awkward, unsettling way. Built to slow you down and at the same time to encourage you to go faster, this act is full of contradictions.
This must be the result of the SRB2 team trying new concept.
After seing ERZ Act 3 carefully, I cannot help but feel pity foor the stage while at the same time knowing it is the hardest of all, because of its novelty (no racing introduced before), because of its placement (at the end of the deadful ERZ Act 2 it is just stretching the pain), and because when you will lose on it, back to ERZ Act 1 all over again.
You guys should rethink your concept entirely. Egg Rock Act 3 WILL absolutely destroy any newcomer, especially those that were not aware of it before hand, and play to not lose. It is so awful for all the wrong reasons to the point where it is almost genius. I am in awe.
And I cannot comment on the Metal Sonic boss fight itself, but I heard it is hard to play correctly, without tanking hit. On that I just say maybe make the good strategies to use against him be more evident and not too demanding. also the border of the stage are electrified, but to be honest I feel like this is in the "manageable" category of things, so... meh.
Sometimes I may go on the opposite routes of my usual run to see how thing are there.