I seen Adventure Time and came running.
Adventure Time is one of the only good cartoons out there right now. It mixes childish animations with deep plot, the backstory of Adventure Time is actually one of the most tragic things I've ever seen in a cartoon, it goes to a level where you're constantly searching every episode for hints of the past of the world, because the creators are just throwing them here and there and it's all eventually unraveling into a story line that's got millions gripped right now. The world they are in, Ooo, was once Earth. A nuclear war happened and mutants rose out of the fallout, creating the creatures there today. There are certain survivors, such as Marceline and Simon who's stories still have yet to be told ( An upcoming episode is expected to do so. )
If you don't watch Adventure Time, I heavily recommend getting into it. Watch a couple of episodes, ask around online for the episodes you should really watch, and I guarantee you will love the show.
People call it a childish cartoon; try it out and see for yourself.