Too many SFnal aliens aren't really SFnal at all.
Many "aliens" are (in the video format, literally) people in rubber suits and makeup. That's fine where the story is as much allegory or satire as SF -- see my post on trope aliens. It's far from fine when we want to broaden our horizons a bit. After all, isn't one of the joys of SF broadened horizons?
Some argue truly alien aliens don't work in stories. If the author succeeds in portraying a truly alien alien, the reader won't be able to relate. Agreed: that can happen. It doesn't have to, as can be proven by example.
That is, some wildly popular pieces of fiction involve truly alien aliens. To name a few:
* The Buggers of Orson Scott Card's Ender's Game series.
* The Puppeteers of Larry Niven's Known Space.
* The pack-intelligent Tines of Vernor Vinge's A Fire Upon the Deep.
* The uplifted dolphins of David Brin's Uplift War series.
In this new series of posts, I'll be looking at alien aliens. Some of the above examples will surely crop up. So will aliens I've perpetrated in my own writing.
Will the aliens to be discussed have any characteristics in common with humans? Most likely. Common physical-world constraints and similar (not necessarily identical) evolutionary pressures may lead to some shared attributes. Beings able to take a holiday from physics and biology would be truly alien -- but they wouldn't be believable.