First things first, I totally love crossovers (I've seen Freddy vs. Jason, Alien vs. Predator and the first Jimmy Timmy Power Hour. I also have enjoyed both Super SMASH Bros games and the first Kingdom Hearts) so when I heard about The Grim Adventures of the Kids Next Door, I got interested!
I at first had trouble getting the episode (living in Sweden, the episodes usually air months after it's shown in the US... and we always have to stick with horrible dubs!) but then I found a link to it and watched it!
Both are really cool shows, so I was certain I'd like it, and I did! The jokes are clever and the script's awesome!