At first, I didn't want to watch this show because of the animation, but I watched one and realized my horrible mistake. This among one of the best shows on CN, and is almost as good as Regular Show (though my favorite between the two is Regular Show).
The show is humorous, set in a fantasy world, the main villain Ice King is very complex when you think about it, I enjoy Finn and Jake's adventures. The only time this show shows any darkness is when the Lich is the main villain of the episode.
Overall, this show is amazing and it is one of the shows that redeems CN in spite of all the crap they've aired like Incredible Crew. and Uncle Grandpa.