The Biology in Science Fiction blog has a nice discussion about the innate “humanness” of most aliens in science fiction.
But at least a touch of humanness is necessary, I think, if you want your human characters to have meaningful interactions with the alien characters. Even Lem’s alien ocean had to know that humans are another intelligent species and understand us enough to tap into our minds. I suspect that the greatest hurdle of our first first contact may actually be realizing that we should be trying to communicate at all. And even once we’ve settle on a physical means of communication, there is the difficulty in fining a common “universe view” – something that can even be a problem between different human cultures.
I agree with one of the commenters that most fictional aliens are really just a reflective lens for humanity anyway.