The great thing about science fiction is that it gives us the ability to confront old questions in new ways. Or at least good sci-fi does this. Sometimes it just uses the audience's suspension of disbelief to bring out all the neat toys and then fails to do anything interesting with them, such as with Spectral.
Something mysterious is killing American peacekeeping troops stationed in Moldova. The only clue is bizarre apparitions visible only through specialized hi-tech optics. The scientist who developed the goggles (James Badge Dale) is brought in to help identify and counter these rapidly spreading entities. As their threat grows, the nature of these beings is slowly revealed, but can a way be found to stop them?
A lot of things go right for this film. The look and feel of the military base is done well. A lot of the character beats are predictable, but still well acted and with decent dialogue. The primary protagonist, Dr. Mark Clyne is definitely a nerd, but is thankfully relegated neither to the naive and nebbish (Steve Urkel) nor annoyingly charismatic (a la Tony Stark) end of the uber-competent engineer scale, but is somewhere in between. Not every film is able to do this.
The first two acts of the film actually do a pretty good job establishing characters, the setting, and hinting at the stakes. It makes it that much more unfortunate when everything just falls apart in the third. Almost all the answers are dumped unceremoniously dropped in the characters' laps and a big, contrived, poorly executed action scene plays out. The reveal as to what's causing the threat and how to stop it is a bit ham-fisted. The improvised weapons they use look like Doom cosplay props. The internal rules they set up are either vaguely defined or just completely inconsistent.