I think you just mean action/adventure cartoons. And I agree. When Avatar: The Last Airbender first came out, I thought to myself, "Why doesn't Nick do this more often?" Say what you want about past Nick compared to current Nick, but there is one thing similar about them - prior to Avatar, they pretty much just focused on comedies and teen dramas and had no action/adventure staples. I'll say the acquisition of TMNT is another example of this, and also all of the shows they wanted based on DreamWorks movies besides Madagascar (Kung Fu Panda, Monsters vs. Aliens, and How to Train Your Dragon were all pretty action/adventure based)...
Way to go, Nick! It makes me glad to see that they're not going to just stop with Avatar.