MapPacks with a plot and at least more than 6 levels
Unless you have a woman's voice like Ellen McLain and have Melodyne. Then go ahead.
I found that the 'Crystal' tts voice here can do a similar reproduction (using Melodyne again)
I have one kinda sorta planned. I'm not going to say anything beyond that because I've barely started (so it could be a while) and I want it to be a surprise.
Well, I have a mappack in the works also. I'm also using some of the unused dialog from Portal 2. It's called "The Part Where Everything Went to Hell." As for the plot, it's an alternative storyline. After GLaDOS wakes up, she tries to kill you with some of her most deadly test chambers.
The first line GLaDOS says is, "So, was there anything you wanted to apologize to me for?" I won't spoil the rest.
My Work
[spoiler]Maps:
Revenge of the Angry Turrets
Capture the Cube [Co-op]
Capture the Cube 2 [Co-op]
TPWEGTH Sample Map
Aperture Aquatic Testing Center
Aperture Aquatic Testing Center 2
Aperture Time Testing Center
ML's Halloween Trick - 1000 downloads!
ML's Halloween Treat
ML's Combination - 1000 downloads!
ML's Jailbreak Labyrinth
ML's Tricky Teamwork [Co-op]
WIP:
"Capture the Cube 3"
Workshop Maps Link: http://steamcommunity.com/profiles/76561198008890579/myworkshopfiles/[/spoiler]
Shhhhhhhhh... I'm secretly working on a large Portal 2 mod... Don't tell anybody...
My map Lost in Transition is basicly 3 levels, but I bet it will take you as long as 6 levels. haha.
Mapping Since May 21, 2011
Your second map made me and my partner almost want to fall on samurai swords, made up for by the epic original factory theme in the first map and the epic (if infuriating) puzzle in the third map.
Length does not mean greatness, your second map took us like an hour but it certainly was not a fun hour, and that's not even mentioning the vomit inducing visuals.
mine will be exactly 6 maps, while map 1 being the intro and a small introductionary puzzle. I will offer it completely with new media, music and new glados / sphere lines, a little backstory and some ideas no't seen in portal yet. Actually they are an extension on "companion object usage" but it's single player. Ofcourse with a little help of some nice steamfriends for the voices and extra hammer expertise.
I'm now working on the intro which is a bit of a pain now, also when it will be completely ready I only would like to release it if valve clears up the engine so that it can just plug in campaigns with complete sound packs without players having to do console commands. I don't want another dead before dawn beta fiasco.
Right now I'm working on my 3rd map that has faith plates and goo. I'm thinking of making at least 19 test chamber maps, 5 escape maps, 2 boss battle maps (actually I might make more bosses in between test chambers), and add some hidden little extra bits to it. I have some special text that appears in a special area that says, "Lookie, lookie, you got a cookie!" 
My Work
[spoiler]Maps:
Revenge of the Angry Turrets
Capture the Cube [Co-op]
Capture the Cube 2 [Co-op]
TPWEGTH Sample Map
Aperture Aquatic Testing Center
Aperture Aquatic Testing Center 2
Aperture Time Testing Center
ML's Halloween Trick - 1000 downloads!
ML's Halloween Treat
ML's Combination - 1000 downloads!
ML's Jailbreak Labyrinth
ML's Tricky Teamwork [Co-op]
WIP:
"Capture the Cube 3"
Workshop Maps Link: http://steamcommunity.com/profiles/76561198008890579/myworkshopfiles/[/spoiler]
It's spelt Tartartus. If you're referencing the Greek "hell".
I know this, but I'm referencing the decal that they use on one of the pillars, where it is spelled Tartaros.
I remember "[SP] Test for fun" by DaMaGepy having a fair amount of levels. No story, though.