Alright, here's the Tyadran First Impression Critique.
First off, since I have a lot of things I'll be discussing, I want to make clear that I don't dislike your mod. I've certainly seen worse, and you have some neat concepts here. All criticism is for the sole purpose of helping you improve.
Nice palette for the Sega logo.
There are a handful of misspellings in the intro, notably "Wilside" and "its self".
I'm personally not a fan of the hub world. The concept is neat, but the actual tiling and such isn't very attractive. I feel like you were going for a Portal/Aperture Science-type design, but I don't really think it works with all of the texturing gone. Personally I would have just made the hub with a city theme.
Why does the first level you find require a helmet from the second level? This seems like really poor design, especially since the first level I go into presenting me an impassible obstacle makes a really bad first impression.
Summary of tiling issues:
As a note on the shooter block segment for Cyclone in the city level: I think you've hit an odd position where the path to fly through is too difficult, and it's incredibly easy to trigger just one block and get out of the way entirely. I'm not sure what to replace it with (drill blocks, if you're a stickler for difficulty?), but I feel like it needs a replacement of some sort.
I don't know about the rest of your title cards (didn't see most of them) but this one has misplaced text:
This teleporter is broken, and kills you instead of taking you wherever you're supposed to go:
While this placement is valid, I'm strongly opposed to having a single Ice Block to land on at the same level as those spikes:
Two recurring problems with your mod - large, empty rooms, and unreachable yet visible flags:
In addition to everything Tyadran has already stated,
Things I like:
The hub world concept is great, it makes potential for the game have even more options for completion than even the original could have done. The monochromatic terrain and blocks I thought were interesting, as you can hide all sorts of secrets/prizes in the walls of the stage (like how those two evanescent blocks are completely indistinguishable), makes potential for a new type of gameplay we haven't seen yet. The 40 diamond requirement was an interesting way to grant access to a later part of the level after a certain condition was met. For once, players must go out of their way to collect diamonds (which aren't that common). Very well done.
The parallelism between Stairway to Heaven and Highway to Hell (ROCK ON!!) is absolutely brilliant, in that the terrain is the exact same with minor changes in block layout. Reminds me a lot of the time travel mechanic in Sonic CD. The atmosphere is nice and pristine for Stairway to Heaven and dark and menacing for Highway to Hell, which makes sense. However, I think you should switch this (make Stairway to Heaven a foreboding sky level, and Highway to Hell some weird lava paradise of sorts). I say this because take a listen to the two songs; Stairway to Heaven is actually the more somber and bleak while Highway to Hell is quite upbeat. Am I going t0o far with this? XD
Things that need work:
The music used in the intro might work in the hub world, but other than that, I would consider having the new background tracks be less repetitive.
Hub world needs a good background, and if you're gonna go with the monochromatic terrain, think carefully about what color would go best with it. Also, try and make the wall corners less jagged by choosing some tiles with more rounded edges. The rectangular look just isn't visually pleasing.
Dying in the second part of Training of Kid 1 makes you have to do the entirety of Training of Kid 2 all over again. I suggest fixing this as this is a major annoyance and something you don't want in the first two levels.
Tar Pits: The default spawn point in the level is right below where the exit telepad is, making it very easy to complete. I suggest moving one of the two.
Luna Caverns: It's probably unfinished, but it's good work so far. Make sure to fill in the large expanses of empty rooms in with something, and maybe have the telepads lead to more varied places.
A Forgotten Past and A Glimmering Future, other than the names and themes, I don't see any similarities or parallels between the two. If you can find a unique way to link the two levels together, this would be super cool.
Firewall: looks largely incomplete, and that one really tough section with the lone rubber block followed by the imp in the narrow corridor needs to be removed as it's way too difficult.
The boss: Juggernaut needs to be secret or very hard to bring into this level because he is absolutely broken when it comes to bosses. If you shoot a skull while the muzzle is inside a head's hitbox, the boss will take damage for every frame the skull is inside the boss head. Unless you want the bosses to be this easily defeated, I suggest you change that.
Tyadran also wanted me to tell you that it's better to post your files on the wiki as .ips rather than .bin for legal reasons, as direct reproduction of a game's rom is illegal or something (from my understanding) and .ips is a good loophole. We just want the wiki to be in the clear for this sort of stuff, that's all, and Tyadran can help you out with that if necessary.
Overall good progress on the mod, just needs a bit of an overhaul, and I think this could actually turn out to be awesome!
As an additional comment, I think you should decrease the number of different helmets in each level. Changing forms so rapidly has an I'll effect on the pacing of the level, and makes it feel inconsistent.
Levels with lots of helmets should be rate, and done with a purpose (see Twelve Tasks of Hercules in KCX).
I was thinking about putting the Training of the Kid 1's teleport higher up in the Appson Hub so you don't need sky cutter in the actual level so you can die without having to back track, I just haven't got round to it yet.
In regards to the Appson Hub, I wanted to give it a very bland and jaggered look to give the feeling that the technology is used as a game any more so it isn't asthetically pleasing and then the 'normal' wildside levels are still deep within the world.
As for The Tar Pits, it completly skipped my mind that you could use Skycutter to get the teleport at the end. I'll probably put a roof on the first room.
The reason many of the levels in that section seem so bare is because I didn't want to give out too many diamond else it would make that whole section too easy and I didn't really know what else to fill the areas with. I suppose I could add some teleporters to elsewhere levels but the issue regarding what to put in there instead of P blocks still remains. I guess I'm going to have to think of some more challenges to put in the empty sections. And that teleport at the beginning of Luna Caverns is supposed to take you back to the hub but I must have forgot to put coordinates in.
I didn't realise Juggernaut had the problem with bosses. I'll make a few changes to that and the murderwall level.