Well, provided I can get this goddamned GML engine working up to snuff, so to speak, its in the works.
Sonic 2 is perfect, as far as I'm concerned. Easily my favorite of the trilogy. I like that Chemical Plant comes out of nowhere. After all, - Planet Mobius doesn't make any sense- cough cough, flying islands, two tailed foxes, cough cough. - If Robotnik is ruthlessly industrializing the planet, why wouldn't there be chemical plants next to natural areas? With some scene transitions, like in the later games, it would probably make perfect sense. Consider what Sonic 3 & Knuckles would be without the transitions. Flying Battery and Carnival Night would be completely non-sequitur. But then again, I prefer all the levels in Sonic 2 over Sonic 3, so I guess the odd juxtapositions don't bother me as much.
I would only switch Mystic Cave and Hill Top around, because I see Mystic Cave's railroad theme leading to the city. Dust Hill would sit nicely between MCZ and CNZ to further the Vegas parallels.
Love the Dust hill/Casino Night suggestion. EDIT: Maybe Dust Hill after Casino Night, to separate it from Chemical Plant? Anyway... switching hill top and Mystic Cave, I dunno about that. You kinda want the extra separation between HTZ and EHZ... as it's been pointed out in this thread already.
If I were to redo the level order, I would do it like this: 1) Emerald Hill 2) Aquatic Ruins 3) Mystic Cave 4) Oil Ocean 5) Chemical Plant 6) Casino Night 7) Metropolis 8) Hilltop 9) Sky Chase 10) Wing Fortress 11) Death Egg. After you run through the hills, you come to some ruins. Then you find a cave that leads to an oil rig. After leaving the rig, you find the plant where all the chemicals and the oil are being prosessed. Then you wander into the city. Then you find the big city/factory. Then you leave the city and climb the mountain to catch the flying fort. Then he gets onto the Death Egg. 4-7 may be outplaced a little bit.
I actually agree with what Keith Stack said and think the level order is fine the way it is. I wouldn't want to play all the natural levels back to back and then all the city/industrial levels back to back. I like a bit of variety and don't think it is all that far fetched for factories and such to be near forested areas. Though since someone mentioned S3&K I'd like to mention that I found Carnival Night Zone to be completely out of place. Clearly the previous level and the level that follow are mountainous regions so why is there a random amusement park up in the mountains? Assuming Eggman built it you have to questions his reasons why as well as how he built it so fast. Clearly he's busy trying to fix and re-launch the Death Egg all while dealing with Sonic and keeping up his facade with Knuckles. So how does he have time to build an amusement park and for what purpose could it possibility serve?
He just wants to have fun... THERE'S ALWAYS TIME FOR FUN!!! :v: I bet that fat fuck had fun when we all got stuck at that barrel... Curse you Robotnik!
The levels never made sense to me either, but getting to that speed in Chemical Plant that early on was so worth it.