Season 5 hasn't actually started yet. It begins on the 29th of this month though, so get ready!
Spoilers for all seasons, and the S5 trailer follow!
It looks like we'll be seeing a lot more of Darth Maul in season 5, based on the trailer. He'll be dealing with Death Watch and possibly recruiting (or scouting) on Coruscant as he gets ready for the ultimate battle with Palpatine... which, by the way, looks so awesome!
I'm also super excited to see where they go with Asajj Ventress. She's turned into a really interesting character, and now that she's been betrayed by the Sith, the Nightsisters have been killed, and she had teamed up with Obi Wan at the end of S4, I really want to know what she's going to do next. From the trailer, it looks like she'll be becoming an antagonist again.
And I think they've said that there will be a few characters dying in this next season. I have a horrible feeling that it'll be a clone (probably not Rex if there's a season 6), the Mandalorian leader chick who's name I can't remember, and a jedi. I honestly think they might kill off Ahsoka. That would really suck, but something has to happen to her...