I have Netflix and watched Planet of the Monsters some time ago, but I did not get around to watching City on the Edge of Battle or The Planet Eater until today. After finishing Planet of the Monsters and I didn't say "I can't wait until I can see the next one." Now having watched the trilogy, I think Planet of the Monsters was the best of the bunch. City on the Edge of Battle and The Planet Eater are a pair of talk-fests with endless attempts at "profundity speeches" that your average 12-year old could see through.
I think that belief was too strained in the motivations of the two alien races, the Exif and the Bilusaludo. The Exif are doomsday worshippers, it's surprising they haven't sacrificed themselves to Ghidorah long before now. The Bilusaludo seem all too willing to embrace the nanometal, even though its continued spread will kill the planet they want to colonize. They reminded me of Elves and Dwarves from Tolkien, so I cannot give the filmmakers credit for any originality.