Cartoons have really mostly improved over time to be honest, I think we just all have our nostalgia goggles strapped on a little too tight. Probably my three favorite cartoons ever are Adventure Time, MLP:FiM, and Flapjack, all of which are ongoing or very recent.
Anyway yeah, seasons 1 and 2 of Adventure Time are basically some of the best things I've ever watched. I f***ing love this show.