And that's why the Modern sections in Generations 3DS suck.
If there's one thing I want to say, it's implement a proper difficulty curve. YES, OVERBOUND, I AM LOOKING AT YOU!
I mean, look at every Classic Sonic game. Green Hill is probably the hardest first level, if only because of a couple of bottomless pits (which you have to go out of your way to find) and the spike bug. I mean, yeah, I consider Sonic 1 to be hard relative to Sonic 2, 3K and CD, but whatever.
Anyway, you can't tell that the game is getting more difficult, which is a good thing. I'm not saying that you should make the game a breeze; you should be trying to make the game gradually support the player less and less without completely letting go. For example, we've all played Emerald Hill before. It's easy, right? That's why it's the first level. After that you are thrown into Chemical Plant. You notice it's a little tougher, but no big deal; the only thing that's really gonna catch you out is that bottomless pit before and during the boss of Act 2. Now, this is perfectly fine difficulty transition. Now, say we go from Emerald Hill to Wing Fortress (I'm not using Metropolis because we all know that shit is cheap as fuck). Holy fuck this is hard. I mean, you may not think so, but imagine you're playing Sonic 2 for the first time; you've been whizzing through EHZ like the cool kid you are and you feel confident about it. Heck yeah, you just beat the boss! Time for the second Zone, Wing Fortress (this is an alternate reality where we all saw Wing Fortress after EHZ, so just roll with it, OK?)! So, after EHZ, you think you know what the game is about; speed, so you take that into Wing Fortress. Yeah, it doesn't work. You have to be skilled or go slow.
Thing is, though we don't notice it; the game is gradually slowing you down. Think about it; EHZ, super fast. CPZ, gotta watch out in some areas, ARZ, gotta watch the arrows and be careful to stay on the top path, etc. You get it? So yeah, if you're gonna make a Classic Sonic game, always pay attention to the difficulty curve. I may post another one of these rant-ish things later.