Spoiler Level: High
The Nightsister of Dathomir! I'm always happy when something from the books makes it into the TV show. Sadly there are no Rancors to be seen (in the books, they ride Rancors!) but it's still cool.
So, Dooku has turned on Assajj Ventress. I liked how his conversion with Darth Sidious mirrored Vader's conversation with the Emperor from The Empire Strikes Back. Will this fit in with the other ways that Ventress was used in the comics and the Cone Wars micro-series? Beats me, but I kind of doubt it. I'm coming to the conclusion that the previous Clone Wars tales (the comics, books and video games) make up one timeline, and this TV series makes up a completely different timeline. Folks are trying to shoe-horn them together, because for some crazy reason everything is canon in Star Wars except the old Marvel comics. I say, give it up, guys. Enjoy this as its own version of events. Heck, cartoons are the first things to get decanonized when new film projects come up anyway, so it wouldn't surprise me at all if the events shown in this series get contradicted when the live action TV show finally comes along. (Case in point, consider the animated Star Trek, Star Wars: Droids, and Doctor Who's "Scream of the Shalka" as previous examples.)
I also loved that the battle droid commander said "By your command" to Dooku. The notes at starwars.com say that it was a deliberate homage to Battlestar Galactica. Never thought I'd see the day when that happened!
As of this writing, this episode is still available for viewing at http://www.starwars.com/video/view/001176.html.