For me it has to be the Halloween Town world from the Kingdom Hearts series.

1). Out of all the Disney worlds (besides Hundred Acre Wood, as it's a side world, anyways), I find it the one that seems the most out of place, in terms of the overall series vibe.

2). Despite that (my first complaint), it somehow manages to almost always find it's way into every release (except for BBS & I think Re:Coded. Haven't played DDD yet).

3). Somehow a group of annoying brats (Lock, Shock, & Barrel) are just as formidable as Cerberus, Cloud, a leopard, ect. Seriously, WTH!? (I guess this ties into my number 1 point, about the world not fitting).

Yoshi's Island, World 2-5. Damn lakitus kept on preventing me from that 100% score...

The Legend of Zelda: Ocarina of Time: Water Temple - For obvious reasons
Kid Icarus: Uprising: The Ring of Chaos (18) - I actually really liked the somewhat artistic approach in the beginning, and the diversion in gameplay was really fresh, but like the Water Temple, certain limitations (like NO POWERS) means this level can get a bit tedious.
Ninjabread Man - The entirety
Mutant Mudds - Some of those CGA levels are based around cheap tricks rather then good level design with the occasional leap of faith or off-screen attack.

for some reason Halloween town is my favorite stage in KH (only played 358/2 days)
Anyway in KH it's wonderland
COD rust
Sonic any water level
Pushmo the chameleon
SM64/DS Leathal Lava Land

SSBB - New Pork City (Think that's the name)
M & L: Superstar Saga - Joke's End
PoP: Sands of Time - That one part where you're in the bottom of a well
Advance Wars DS - The double Volcano stage
Sonic 06 - The game

Oh, and any Big the Cat stage in Sonic Adventure.

Sonic 1 - Labyrinth Zone, Act 3

Don't worry, I seem to be in the minority in this. I know a lot of people who think it's one of the better worlds in the series (although usually because they're fans of the movie itself).

I just think that the fairy tale/mythological worlds like Agrabah, Olympus Coliseum, Neverland, Port Royal, Land of Dragons, ect., fit the series themes much better.

Blighttown in Dark Souls. Thank God you can skip most of it if you have the Master Key.

I guess I can sorta see where your getting at, I mean TNBC is the oddest Disney movie in KH (unless you count pirates)

the bonus gauntlet levels in battle kid 1...tougher than a 2$ steak

Actually, Pirates is a much better fit for KH than TNBC, IMO. It's a series filled with adventure, action, & magic (perfect for an Action RPG).

Oh sorry I thought you ment visualwise.. Ok yeah there isn't any magic in TNBC.... Hmmm ok

Arlon's Lunar Sanctum in Ki:U. I don't know why I hate that level so much.

I think this level. I don't remember if that was the exact one, but one of the levels in that world or a similar level made me just stop the game because I couldn't beat it and I had other priorities.

nonsense

every ghost house in mario U. loved the game but i'm getting tired of ghost houses. they have become select a random door and see what happens...which is annoying.

The water level in Drill Dozer. That stage was effing awful!

yeah that was...ugh...don't remind me. Weak slow nonsense for an otherwise fantastic little game. I mean, it was at least clever how you controlled underwater but...

Also, while the lower areas were fine, I do not like Dark Torvus Bog. Most annoying bosses, most annoying enemy, purple water of death and is just nowhere near as well designed as its light counterpart or any part of the game.

I can actually agree with most of that, but chapter 18 in Kid Icarus Uprising is actually my favourite chapter in the whole game! I love the gameplay diversions. Also the end if the chapter is just epic IMO.
For levels I hate, it's the majority of levels in Mutant Mudds. Don't get me wrong, I love the game, but lets just say I've shed a few tears of frustration on the brutal difficulty of some of the levels!

Marble Garden zone in Sonic 1.