Hello! I'm late to the party in terms of providing feedback on your pack. I'm kinda scatterbrained with my schedule, so most of my time I spend on SRB2 is in general discussion or with SRB2DB. It seems you're unopposed to editing your old levels, so I'm going to go through each zone and list everything that I think is worth mentioning.
Oh yeah, before we begin, I hate cutscenes. Most cutscenes made to go with SRB2 levels feature almost entirely text, when cutscenes need good backgrounds with the characters doing stuff. Most people don't really care enough to make that art. The text itself is never essential to the levels, most of the time attempting to weave Egghead in as an explanation. Don't worry, your pack will be fine without them. We won't be lost or wonder why we're here. We all know why we're here: we want to have fun.
SUNSHINE ATOLL, BABY!
My first problem I notice is your hallways. You frequently have long stretches of mostly flat land with some variation. It's as if you noticed that hallways are bad, but instead of removing 'em you just dressed 'em up and made 'em look pretty. You really don't have to get rid of ALL of your hallways; room to run is fine, and it provides gameplay variety. You have too many hallways though, so you gotta get rid of some. I suggest starting with the low-ceiling hallways.
My second problem is more of a nit-pick. You get a lot of your jumping from placing a lake in the middle of the player's path and asking them to jump over it. It's fine gameplay, it just feels lazy.
In contrast, my favorite room from this zone is this one. Can you see why?
EEERUPTIIOOOONN COOOOONNDUUIIIIT
Act 1, MAP04, about (3144, 2724), Sonic can't get out of that pit.
SSN said that if you use the same texture for floors and walls, it's harder to see where you're going. At the beginning of Act 1, the dark red rocks that are both walls and floors make it very hard to see.
Act 2, MAP05, about (8111, -715), my framerate is sketchy. It's playable, but I'd like it if you looked into that room. I'm running software at 1280 x 1024.
Also, Act 2 has some hallways I don't like. If you can, remove some please. I realize that sometimes hallways are necessary because of how the rest of your level is layed out, but removing every hallway possible would help the pacing of your level.
I dislike the crawla commander fightin Act 2. The problem is mostly that SRB2 isn't built for combat, with enemies serving more as obstacles than antagonists.
I dislike the yellow globs which fall down. If you tweak it to perfection, it could be a workable gimmick, but at about MAP05 (7016, 4931), it's so thick that it's random whether the player takes damage or not. I either spammed invincible time or skirted alongside the edge of the room to get through.
My framerate is also tainted at about MAP05 (1231, 6392). I'd appreciate it if you looked into it.
MAP05 (-985, 6265), that elevator is confusing. Why aren't the buttons inside the elevator?
MAP06, my framerate is tainted again. I'd suggest less linedefs for the circles.
DrownTown
I like your mossy bricks texture. I was surprised when I couldn't find it in srb2.srb. It's so awesome, you should submit it to the suggestions topic. No, I'll do it for you.
Your graffiti terrifies.
Your streets are glorified hallways. I'm not sure if you want to fix that because the streets are crucial to theming. If you get rid of the hallways on your other maps, these might be refreshing in contrast instead of boring.
At about MAP07 (-3362, 489), I have a vendetta against that room. When I think of your levelpack, this room comes to mind and convinces me not to play it. If you like some of the ideas, rework them into a better layed out room.
One of my pet peeves is "one way" signs that don't point towards forwards. I know they're just decoration, but it still bugs me.
Oh, hey, nice sky! I didn't see you there. Go split it up into several different patches so you don't get that white band across the bottom. Make your patches horizontal bands which are 128 high. I suggest SLumpEd for messing with TEXTUREx and PNAMES.
MAP07 (1576, 11743), that "waterslide" makes me face the wrong direction while I'm using it.
Act 2, right at the start, it took me a while to figure out I where I was supposed to go. Was that intentional?
I play as Knuckles when I can, so underwater sections bug me because I can't thok back to normal speed while I'm underwater. I move reeeaaaaallllyyyy slooooowwwly underwater. When I'm not underwater for very much at a time, it's fine because it's not really a big deal. But you have hallways
underwater. That's unbearable.
I'm not really diggin' that waterslide. The waterslide-wave is fine, though.
I
am diggin' that Disco Egghead sign.
Oh yeah. If you want to kill the player in your levels, you've got to give them enough lives to survive. Go sprinkle some more 1ups everywhere. It'll make the player's life easier so that they're not so afraid of death. I'm runnin' two lives right now, and I'm kinda worried I'll gameover and have to warp back to where I started.
In Act 3, hide the "skims" behind the wall. I bopped a few before the water rose where they are now.
Okay, it might just be my headache, but I'm done. The only thing I can muster right now is apathy. I quickly skipped through the beginnings of each Act 1 just to see what was there and was sad to see that each level seemed about the same level of quality as the Ice Zone. Honestly, are you just pumping these things out like crazy just to have them done? Maybe I just care too much about mapping to let myself churn out content like a zombie, but that's a lot of content you have at a pretty mediocre quality. Have you just not gotten around to remaking the last four zones?