That's all well and good but SRB2 Sonic is still heavier than SA1 Sonic which was my point, if you're going to claim that SRB2 is too floaty in contrast. I guess I should've specified air physics. SRB2 was just a good example as the only 3D Sonic fangame I've played that properly carries forward mechanics like badnik bouncing into 3D.
Does Sonic truly need to control exactly the same, or even an approximation of what the classics were like in 3D though? Many successful 3D entries in previously 2D games control vastly different. Metroid Prime, 3D Mario, etc. all do a great job at adapting core philosophies of their inspirations without sticking 1:1 to physics and gamefeel
I said earlier that the floatiness some fangames have isn't an inherent problem, but also that it doesn't even apply to SRB2 which has heavy Genesis gravity yet still works. Either way can work depending on the overall game design! I'm not insisting the controls can't be floatier than the classic default, like what's apparently so problematic about every 3D Sonic fangame.
All sonic games should be like frontiers where each falling state has a completely different gravity parameter, of which there are three of them. Godspeed sonic team
The main problem I see with every 3D Sonic games can be summarized as this: Why bother running on the bridge when you can easily jump and float over the water? At least, Sega tries to avoid this issue with 3D level design and some 2D sections, especially in Frontiers. But this is not an easy task. They often fail to do it just right: too many corridors, too many bottomless pits, too many scripted sections. On the other hand, this is Mario: Good 3D level design here. It is actually easier to take the bridge.
Greenflower's level design is like 30 years old at this point and was bound by the slopeless Doom engine limitations of the time. Most agree it needs a remake and is already getting one. Though in that case I think it works. You're supposed to be able to skip up that little waterfall on the left as a shortcut anyway. You're meant to try other ways besides just crossing the bridge.
Put a little treat on the bridge, to give the player incentive to cross it the old fashioned way. That's also how I'd address the "but why would I go through the loop?" question.
These examples perfectly illustrate @Zephyr's point while also countering it in a way. It's easier to cross the bridge, but just about the only upside there is to it is the convenience. Everything else of note is happening everywhere else in your field of vision. The mission structure also makes it so that convenience is sometimes preferable (like when you're racing the Koopa), but sometimes not (like when you're picking up coins, so the one at the top of the platforms on your left becomes more interesting). The mission structure by itself also makes it so that asking "and what might be under the bridge?" has merit even if there's nothing there. There might be a star there! Who knows! So sometimes a treat on the bridge might work. Sometimes not. It's not just level design as a separate discipline from all the rest of the game's objective structure, life system and how it handles your attention. It's not very different from how, in not just a few classic Sonic stages, upper paths are convenient, but generally harder to stay on (because gravity) and more barren than what's below, which is more dangerous but also filled with stuff you might want or need. Carol Yas has a whole lecture on this kind of stuff.
There's already a line of rings on the bridge in-game. That area is kinda boring and flat along with the rest of Greenflower Act 1 but its problem there certainly isn't that you have other platforming options besides crossing the bridge. You're supposed to be able to progress however way you want throughout the entire game. When I look at it through that lens I just see a well-designed microcosm of how you're supposed to engage with the rest of the game. Playing as Tails or Knux, the play experience in that section immediately becomes different. Why bother crossing the bridge when I could have more fun flying or climbing up to see where that waterfall goes? The level design forcing you to cross the bridge would be going against the whole fun of SRB2 (and 3D Sonic as a whole) if you ask me.
This kind of just proves the point myself and Blue Blood are making. Pretty much every time Sonic is in the air in that clip occurs as a result of the player's knowledge and mastery of the game's mechanics and level design, abusing terrain as in the classics to get that air time and skip level segments. It's not intended, but it's much closer to the execution of the concept in the classics than the likes of Frontiers, Utopia or Green Hill Paradise are because Sonic's ability to gain height is increased in Adventure, as well as his downward velocity so, outside of some very clearly unintended skips, you don't get these borderline cartoonish launches and the time that is spent in the air feels in much better proportion to the time spent on the ground. And that's the point, really - the ground is where the gameplay actually happens. A perfectly 1:1 translation of the classic physics is almost worthless to me if it means the game becomes 90% iar time with no interaction or engagement for 10% very straightforward terrain manipulation (with Frontiers, the spindash is so OP that such an act barely even qualifies as manipulation).
Utopia and Green Hill Paradise both stick you in singular, circular skatepark environments that don't even have end goals. Of course they're going to take every opportunity to fling you up into the air and make the most use of that limited space, in the same way skateboarding games do. It's just not a problem in of itself, and doesn't apply to all 3D Sonic fangames with momentum in mind anyway.
I personally don't find it a problem that there's more air time, but if there's going to be more air time, it'd definitely be good if that air time involved something beyond itself (as exhilarating as it is in itself to make Sonic do big jump). Launching off of a slope is a kind of jump. Why do we jump in a platformer? To avoid an obstacle or a hazard, to acquire something, to reach somewhere else, etc. A Sonic who has a lot of vertical mobility would gel best with some very vertical level design with some goodies hidden up high, or some large chasms to leap over. Or give me some rewards for simply having long airtime. Maybe points? An elevation tracker and achievements for reaching certain vertical milestones off a single jump? The higher you fall from the bigger a shockwave you send out once you land? If Frontiers wants to lean into enemies having HP, then have drops from higher up deal more damage to things you land on, same way I think you should deal more damage to them the faster you're going when you roll into them. I think there are definitely ways to have our cake and eat it too. Just gotta find the right fork.
Green Hill Paradise fucks me up not because of air time, but because it keeps warping the ground and trying its best to disintegrate my sense of place. Sonic has no vestibular system, you know: constantly warping terrain like that does nothing for me. As warped as terrain can be in 2D, your orientation never changes, thank God. And even in loops in 3D games that have what Azookara called the vomit cam, you know you'll end up with the same sense of place as before. In any case, Zephyr is right. We really can't judge how good a framework is just by the motion play. The objective structure, the overall loop etc. are just as important. Level design doesn't just exist in a vacuum. I'd like to see a 3D game that claims to be classic-inspired, even one with ample airtime, to firmly establish up or down as a new general orientation (kinda like SA2's Green Hill, where if you're in doubt, go down). I'd like to see how that goes. But that's still preserving an A-to-B structure, and that changes everything. We don't necessarily need to do that. The airtime can be an asset.
