I remember Alien Nation, heh. I always just called them the Sponge-Heads, lol
While entertaining, I think the main reason I never was able to get into the show was the fact that it is hard for me to enjoy anthropoid aliens (little green men, grey skinny men, _______ men (fill in the blank)). That is one of the prospects of District 9 for me, because they are so non-human. I know appearance isn't everything, but I really like the more monstrous entities when aliens are concerned.
Anyway...that was a ramble, sorry heh