Season 7 just started with a week of new episodes and later this month we'll have an 8-part miniseries focused on Marceline.
I'm very excited, partially because that's 13 episodes after what seems like a long break (and Season 6's schedule was frustratingly erratic and protracted, with multiple breaks between premiers), and mostly because the episodes we've seem so far have been a return to form after a season that leaned maybe a bit too heavily on melancholy and experimental episodes. Despite the craziness and mythology the true strength of Adventure Time is the characters, so it was great to see a fantastic Bubblegum and Marceline episode (Tuesday's "Varmints"), a back-to-basics Finn and Jake adventure (Thursday's "Mama Said"), and a frighteningly funny examination of BMO's inner life (Friday's "Football," which was my favorite of the new episodes).
It's hard to believe the series has been on for six years at this point! I'd say that officially makes it a "long running series," especially in the ephemeral world of cartoon shows. I still remember getting into the show back when the first season was ending and the second was beginning. I quickly realized this was something special.