I've commented on this before, but I think it is strange how Hollywood converges on similar topics, themes, and archetypes. Dark City is a film noir + sci fi. It's pretty good at both genres.

Our protagonist is John Murdock. He's searching for his memories and sanity in a world that is always night. He's being pursued by aliens disguised as humans and humans that are currently playing the roles of detectives.

The aliens are gelatinous, jellyfish like creatures that are living in human hosts. They are a dying race trying to divine the essence of humanity. They do this by studying the humans and messing with their memories. Murdock is only slightly aware of this and is trying to break out of his 'prison'.

Worth watching.