The final scene of the Technodrome features its descent/crashing into the ocean (a slap in the face homage to the 1980s cartoon if ever I�ve seen one!)
Kraang Prime has some parallels to Krang from the original 1987 cartoon. Their robot bodies both have similar-looking heads and Kraang Prime at one point refers to the Turtles as "miserable mutants", an insult the original Krang used against the Turtles a few times.
The climax of the episode is almost identical to the season 1 finale of the 1987 cartoon. (The turtles fighting a giant Krang in an exo-suit while Splinter and Shredder face off)
The Reveal: We find out that the Kraang needed April's unique mental energy, and they tried to use it to attune the planetary mutation mechanism to the Turtle's reality (as it was mentioned earlier that the mutagen didn't work like the Kraang thought it would on Earth).
We also find out the Karai is actually Yoshi's daughter Miwa and the Shredder has been telling her the reverse of the truth: that she's his daughter and that Yoshi was the one who killed Tang Shen out of jealousy.
Sequel Hook: The Kraang ship lands in the ocean, but reactivates, indicating that the fight isn't over yet...