What makes something Anime...? Ah the age old question (from the 90s). I figure what makes something anime-like varies from person to person.
I guess there's first the art style of something. Teen Titans being probably one of the better known cartoons out there with that style. Also, if you happen to read it, Sonic the Hedgehog comics changed into that style somewhere around issue #90 (they're at #150 now).
Unfortunately, it seems like a lot of people consider the art style to be the only thing that makes something anime. With the new show Loonatics Unleashed, earlier this year when the people in charge announced it, they were already saying it was anime. "They have superpowers, they have the big eyes, it's a cartoon, therefore it's anime" was how I interpreted what they were saying.
Teen Titans (TT) I'd have to say is the closest American-made cartoon to be considered Anime or is anime (Don't know about Megas XL because I've only seen a small handful of episodes). The reason why I say this is because TT sometimes has a storyline which separates it from other cartoons. Usually, with American cartoons, you could watch any episodes in any order and it would still make sense. They're kinda like short stories with no connection to anything else. With Anime, there are some things and events connected. With Anime, there are references to previous episodes and characters are seen growing, becoming more powerful and skillful. There are the occasional short stories in anime but there are only a few in between points in the story. TT does this. Example: Robin is attacked by someone, Robin hears about Slade, Robin meets Slade, Robin hunts for Slade, Robin finally finds Slade and battles him again. All of these happen in different episodes and in order.
I think there's more to anime, but right now I think I've gone too far in too many directions. >< (It's morning and I'm not quite awake yet)