This was a hard list to make. I had trouble deciding what sci-fi films qualified as underseen/underrated/overlooked. So I feel like there's a lot on here that people will consider too well known to suit the name of the list, and also maybe a lot of films that people will think are missing. For the moment I've erred on the side of creating an inclusive list, but I might pare it down in the future.
This list is in chrono-alphabetical order, so it is not ranked, although you can sort them by my rating to get a general idea of how highly I value them.