There is no denying it that this is meant for kids, but they actually have a lot of homages and allusions that kids wouldn't get, like cocaine and alcohol usage. Plus the generic slapstick esque comedy is always worth a laugh.

The unique characters, the Imaginary Friends especially, actually change throughout the series, sort of. Things that we learn in one episode actually are referred to in another. again, like cocaine, or Mac's extreme hyperactivity to sugar.

If you watch the pilot movie and then some of the most recent episodes, you'll note a completely different character in Bloo. That's not a production error. At first he lived with Mac, and now he lives at the house and with so many other Friends he's changed in voice and personality.

Mac and sugar and The rabbit and carrots.

...for?

Fosters?

Hunter "Foster's" is short for "Foster's Home for Imaginary Friends" where imaginary friends come to life and hang out with kids. When the kids out grow them they leave them at Foster's Home, or abandon them. One kid, Mac, is unwilling to give up his friend Bloo. Although he can stay at Foster's, it is an adoption home, and so he may get adopted if anyone comes and wants him. This has consequently made Bloo the "Best friend ever" and so whenever he does go up for adoption, it is a big deal.

I loved this show when I had Cartoon Network. A little too kiddish sometimes, but meh, that's American cartoons for you.

Btw guess where "Mack & Blue" came from. ;) (...yeah, some people actually don't know about that)

I always kinda got the joke of the name, plus there was that Cheese episode, and many others.