I was just remembering the aliens from the TNG episode "Night Terrors".
The episode showed us very little of them. We only got to know that they are able to send telepathic messages, and we got a quick glance of their ship at the end (some kind of blue glowing energy ship).
I wish they would have expanded a bit more on those aliens. I'm not sure why they didn't.
I'm guessing they probably wanted to keep that creepy feeling all the way to the end? Maybe revealing more of the aliens would have defeated that? I still feel cheated though