A lot of people call Adventure time a show for adults made for children.
Honestly I didn't really get into adventure time until I've seen a lot of episodes and a lot of VERY specific episodes. In fact it wasn't until I heard Marceline's song in the gate episode that I actually started to see that maybe the show was more then just being weird. That maybe under all that weirdness that there really could be a heart, just one it doesn't show off.
A lot of shows can easily put up a façade of shallowness and simplicity but can be pretty deep when you put thought into it. Beyond some obvious example I can even bring up Jem and the Holograms a children's show in the 80s about hair rock.
It is a very simple show (still speaking of Jem) and it is as diabetes enducingly sweet as you can get. If you don't throw up listening to this:
http://www.youtube.com/watch?v=_9Xlbs1cnUs . Then you have quite the constitution. Yet it probably handles its main villains (The Misfits) in the most freakishly fair way I ever seen a western cartoon do, EVER! For being a show for children it manages to be more mature then some non-comedy adult shows (then again... that isn't an accomplishment)
But that is why I like Adventure time. I don't find much funny about it, but it seems to have a deeper character consistency it doesn't throw around. Often what is just a joke actually seems to have a deeper connection with the plot and characters, its humor is often also the same way it tries to deliver genuine character.