Quote Originally Posted by Madonna View Post
They want to rule Earth, I... guess?
No, they quite clearly state they don't care about Earth. They want the Tesseract so they can take over a lot more than just Earth and Loki says he can give it to them. His payment being to rule Earth which he only wants to do anyway because he sees himself as a God and he wants to hit Thor where it hurts.

They lack depth, and because of that, who cares about the aliens?
The aliens aren't the main villain. Loki is. But the aliens are there to provide the Avengers with a rather large challenge to overcome in the end. As such the aliens don't actually need a lot of depth yet, but I'll elaborate in a second.

Also, post-script: in advance, smurf the comics. I am sure they have a rich and meaningful history which go into the alien invasion force and their background, but that was not presented at all in the film I watched.
Of course it wasn't presented in this film. This film was about Loki more than anything else, and was meant to establish that there is more out there than even the Asgardians know about, as well as establish the aliens and Thanos as villains going forward into future movies. Because they will be villains going forward, which is going to be a problem when you consider how hard a time the Avengers had dealing with them this time. You aren't supposed to know a lot about them yet because the focus was clearly on Loki and they will become a major player down the road. You seem to be forgetting that the Avengers film franchises are able to play a pretty long game story-wise so they can get away with introducing them in this film and explaining more about them later when they become the main villains.