I think that's a valid perspective, but one that only works when the show strikes a careful ambiguous balance between the two interpretations. I'd argue that it definitely started out as 'friends having an awesome time defeating evil', but that the dark apocalyptic nature of the world has come so far into the foreground it's impossible to see it solely one way or the other anymore.
I think the idea of the show is to have a show meant for everyone where whoever can take whatever part of the story and use it as their interpretation of the actual show. Some people watch it and just see a story about friends having an awesome time defeating evil, while as others see two survivors of a apocalyptic war fighting to prevent the dark past of the world from destroying the rest of the planet.
I have a different perspective on it. I don't think that it's supposed to be taken one way or the other, but both at the same time (Finn voice: quantum mechanical!). This juxtaposition of supposedly conflicting elements seems to be a recurring theme reflected in the animation, story, and characters, and in fact I believe it's one of the main points of the show. The bright colors on an apocalyptic world, Finn and Jake being cheerful and having a good time while fighting evil, etc. I could write a thesis on the subject. Instead, I'll stop here and say that it's one of the most well executed concepts that I've seen.
Edited by Oracizan, 19 November 2012 - 03:25 PM.