The reason for the Heavy Metal influence is...
...that the concept art was done by Jean Giraud (Moebius himself). I've seen the film a couple of times now, and I always enjoy it (though I would refrain from anything so bossy as telling others they should see it). It's got several people in it who I enjoy watching. And I do enjoy the various peeks at a potential future.
On the negative side, the main quest that the plot is built around is a pretty derivative (again, Heavy Metalesque) fantasy/scifi standard. It tries too hard to be too funny at times and the comedy is often poorly timed. Also they have joke-music that they play to accompany the humor which is something I've always detested.