I saw this mentioned on TV Tropes in a way that seemed to reccommend it, so I've begun reading it, and it's pretty fascinating. It's a fan's dark take on the Turtle's lives as they become adults. It's done in a manga style, which is sometimes annoying, but it's thankfully not as annoying as I thought it would be. So far it kind of goes a little overboard with the emotions, but then again, the Turtles haven't really had an unbelievably massive tragedy before.
http://www.obscurezodiac.com/chapterindex.php

I thought the comics were actually pretty dark and filled with emotion and dark periods.
I know the one I read a few years back involved Raphael going to the funeral of some warrior bear thing, and another involved April realizing she wasn't human. And Casey is just fething psychotic.

oh man, I just found out there was a TMNT megabloks set and now this!

No, but one of them is a writer under an alias.
After reading more of it, the story is becoming more and more interesting. A new character is added that you come to care about, and a familiar man with a baseball bat is reborn through a younger generation.
...but don't worry, because Casey's still around.

Weren't the original non-Archie comics already pretty dark?
I know volume 3 was. I loved vol. 3 as a kid. Donatello falls out of a helicopter, shatters his shell, and only survives by becoming a cyborg. kEwL.

I've read up to the most recent update. Man, for a fan production, it is surprisingly well-made. I would buy this at a bookstore if it were sold there (of course it won't be, because that would infringe intellectual property). Even the Japanese art style has kind of grown on me with the way they use it in the series. Renoir is a great addition to the universe, as is Shadow. Also, unlike most lame web comics that show no sign of a definite end, it feels as if the story is moving to a powerful conclusion. I am not sure how long it will take to reach it, but the pacing seems to be right where I would want it to be.
I am eager to read the rest of this guy's pages as he draws and inks them. In fact, would it be expensive to save all the images as a PDF and take it to a printing center like Kinko's to print some of these out and put it into a booklet I could read? Would the quality be comparable to the online work if I got it done professionally?

If you want dark. http://www.amazon.com/COLLECTED-Teenage-Mutant-Ninja-Turtles/dp/0981949703/ref=sr_1_2?ie=UTF8&s=books&qid=1263949040&sr=8-2