Season IV has dealt with this quite well. It started with a new development in the romantic sphere, with Finn starting an awkward relationship with the Flame Princess, which largely allows for amusing moments with Princess Bubblegum, who may or may not be jealous. Largely, though, it means the relationship drama gets the impression of being dealt with and can be left to one side, with just a handful of half-episodes devoted to this new love story.
Otherwise, season IV has been remarkable for going back to revisit elements of the series I didn’t expect to see again. I loved the sheer randomness of the King Worm’s appearance in season 1, and never expected to get a whole episode devoted to him, and though it just about worked, I think I would rather have left it as a bizarre season 1 nugget. Not so the revisiting of Abraham Lincoln as the King of Mars, an element from the original Penn and Jake pilot. I even wrote that that sort of randomness was the kind of thing that separated the pilot from the main series, so this came as a surprise – but worked well, especially since he was made real rather than an apparent figment of the imagination.
In some ways these detract from the originally Pythonesque surrealism, taking originally inexplicable things and giving them explanations, but Adventure Time is now a long-running show, and fleshing out the world properly works.
Otherwise, season IV managed to be a good one largely by just sticking to the Adventure Time formula and doing it well. Gunter the penguin rising up as an unstoppable force, Treetrunks having a rather disturbing romantic liaison, Princess Bubblegum creating a terrifying sphinx creature that has to be countered in an epic battle, BMO getting a detective pulp parody episode and Lemongrab returning in truly creepy and socially awkward style all make for great little twists on an established tone, and the occasional moments of great poignancy – like when The Ice King assembling a princess out of stolen body parts gives way to an existential crisis, or when Marceline remembers her childhood in a brilliant and unexpected little twist (that apparently never came up in the Christmas video viewings, presumably because Marceline liked to lurk outside the window) – really raise the series up and make me wonder about the Land of Ooo’s apocalyptic origins. There’s an episode in season V entitled ‘Simon and Marcy’ – I’m very much looking forward to that one.
The series has again ended on a cliffhanger, involving the Lich – brilliantly creepy flickering for a frame or two over Billy, and perfectly voiced by Ron Perlman in Teen Titans mode – and we have only a couple of weeks to wait for new episodes, so I’m very much on board, probably for the rest of the show’s run.