I am only commenting on the Grim Adventures of Billy and Mandy. I have not seen Evil Con Carne.
I try to watch this show as often as I can. I watch it in the morning just before work to get me in a good mood. I can think of nothing like it. It's hilarious, gross, interesting, extremely clever, etc etc. I don't think little kids will get the humor, some of it is somewhat suggestive, but a lot of it is very slapstick. This show has some subtle humor masked by lots of physical humor and some GREAT sound effects, the essence of cartoons IMO.
I has some excellent guest characters, like Hoss Delgado, Eris the Goddess of Chaos, and Irwin. Many of the episodes have a theme based on a myth, either ancient or modern (the coming of Cthulu for one). These episodes take such serious topics and twists them into something absurd and absolutely hilarious. I particularly enjoyed the episode where they looked into the future and Mandy was a caterpillar-like entity who was immortal and ruled the universe, using cinnamon as her source of power. This was a parody of Dune, more specifically the fourth book of the series, God Emperor of Dune. That's just one of the examples of the show parodying somewhat obscure themes or stories.
One of my favorite episodes was when Voltaire was a guest and he sang his "Brains!" song on it. Very entertaining.
Some people might not like it at first. I agree it can take some getting used to. Just watch an entire episode or two; if you have any sense of humor you should find it very entertaining.
