It's also weird seeing Shredder with a daughter, though I think I know that he had one on the 2003 series. It's cool that they worked Krang into this series with The Kraang species (which combine Krang with the Utrons). Also interesting how on the original series Krang could talk to Shredder while his body couldn't, but on this show the Kraang's can only communicate in english when inside their bodies.
*Face Palm*
Karai is a character from the original comic book. She was also prominently featured in both TMNT 2k3 and the 2007 film. She's also in the IDW comic as his granddaughter (I don't know if they elaborated on it, since I missed out on Secret History of the Foot Clan). In the 2k3 series, it was explained that she was a homeless little girl that Oroku Saki took pity on and adopted her, leaving her to deal with loyalty to her father for saving her life and the Turtles for realizing Shredder was basically using her. She goes for the former through the end of the series. They haven't revealed anything about her past yet, though they hinted at something strong when April said her mother died (or was missing, I can't quite recall how they stated it).
As for the Utro
ms, there's no doubt that the Kra'ang are supposed to be a darker interpretation of the characters. Utroms in the old comic and 2k3 series were peaceful and just wanted to go home... in IDW continuity, they're at war with the Neutrinos (now older warriors rather than young teen beatniks) and lead by Krang.
As for Don's crush on April, that's an extension of the last series. It was very subtle, as April reverted to her
real job of being a scientist that worked for Baxter Stockman, and Don found her a kindred spirit as he's still an accomplished scientist (ironically, he's one in every continuity
except the original comics).
Seriously... that 1980's cartoon, while I can't say anything negative about it otherwise (except for thos
e terrible European Vacation episodes), it successfully killed the legacy of the original comics for a generation. The comics are far more interesting than any of the animated continuities.