I've came across this amazing video while browsing around Behance. It's an over minute long set of illustrations nicely animated in After Effects.
Star Drive Aliens from Matthew Oswald on Vimeo.
I'm not going to talk about how detailed are these creature/characters, as they were created by Nick Wiley. I'd rather concentrate on animations, which were done by Matthew Oswald. He stated using only After Effects in this project and posted a 20secs loops for each section (can be viewed here). Maybe these animations aren't that complex, but definately requires a deep understanding of how AE works. It also gave me idea of another way in which I could animate more complex illustrations.