I suppose the organic feeling comes more from nostalgia (or the use of the different biomes). SA2's stages were decided by the story, which made it feel much more organic, since they weren't separate places but actually strung together by an ongoing journey.
Just because the story says: "Hey, we're in a jungle. Now we're in a desert. Oh now we have to go to outer space!" doesn't make it more organic at all.
Oh, and let's not forget that SA2 has 32 stages in total (counting the unlockable Green Hill Zone one), and 9 of them have a generic space-theme. Nearly a third of the game has exactly the same theme.
SA1's hub exists for the sole reason of making all the stages more organic. There's an actual world established, and all the stages fit into that. The game doesn't simply load up a theme-park level because the story demands it. You actually go where that theme-park is located in the hub. With some levels, you enter them in different places with different characters, corresponding with which area of the level that character gets. For example, Knuckles' Speed Highway stage only consists of the streets (which is the last segment of the stage for Sonic), so instead of entering Speed Highway via the skyscraper elevator like Sonic, he enters via town hall, which is where Sonic exits.
Pfffffffffft hahahahaha
Yeah, only 1/3 of SA2 is enjoyable without being ironic; at least half of Adventure is good.
And the shooting in Adveture 1 didn't SUCK SHIT
This. The only aspects of SA1 that I can see people arguing as being bad is Amy and Big. And if all you're concerned with is beating the main story, you'll be playing as these characters for about 30-40 minutes each. That includes all the running about in the hub.
Here's a breakdown of how many stages each character has, and how long those stages tend to be:
Sonic: 10 stages. All long.
Tails: 5 stages. All moderate (half the length of Sonic's stages).
Knuckles: 5 stages. Incredibly short.
Amy: 3 stages. 2 are moderate, one is long.
Big: 4 stages. Incredibly short (assuming you're just catching Froggy, and not going for other fish).
E-102: 5 stages. 3 are incredibly short, 2 are moderate.
Sonic's stages are awesome.
Tails' stages play very similarly to Sonic's, so that's a good thing, and help stretch out the speed-orientated gameplay.
Knuckles stages have the good sense that it's successors in SA2 lack; being incredibly short, to the point of basically being a minigame. You're looking at about a minute or so for each one. They're entertaining enough. You certainly don't have enough time to get bored in any of them.
Amy's stages are the weakest in the game, as they feel like a misuse of the game engine. After playing platforming-based levels as Sonic and Tails, going to a clunky character isn't fun. But at least there's only three of them.
Big's stages are the shortest in the game. Even shorter than Knuckles. In three of his four stages, you start right next to Froggy, and catching him is piss-easy, regardless of how much you like/dislike the fishing mechanics. You can easily beat these three levels in 30 seconds each (and that's not an exaggeration; I'm replaying through the game right now). The last level, Hot Shelter takes about a minute, only because you have to make your way to the water area first.
E-102's stages, like Knuckles, benefit from being significantly shorter than the Tails/Robotnik stages in SA2. You don't have time to get bored of them. Of course, it also helps that they're better designed. They're more open, and there's more variety in environments. I enjoy these.
If you're going for all the emblems, I will definitely agree that Big's levels are fucking shit. I'm currently doing them now, and trying to catch a 2000g fish in each level is like pulling teeth. Sometimes they don't spawn at all, you have no idea how much a figh weighs until you've caught it, and you can be struggling to reel in a heavy fish for 5-10 minutes. But if you're only playing the main campaign, then there's no real reason to complain, because none of these issues are a factor.