I don't think any of those are underrated... most of those are rated right where they belong. haha.
A few are "not well known", or "forgotten". I'll give you that.
But yeah, moon. Rated really well. but yeah, its an indie movie, with Sam Rockwell. sure you're average dudebro or soccer mom never heard of it.
Dark city, Strange days. basically up there with Blade runner among critics and cult followings. but yeah, again, not as well known.
Dune, is highly flawed. Alot of valid complaints on that. interesting in that it had a HUGE goal. tried for epic movie making. But kindof fell short. much of criticism comes from "not mah book"
Sunshine great for 45min, falls completely flat at the end. My favorite part is Johnny Storm is a giant asshole, but completely right the entire movie. Its nice to see the asshole, "stay on mission, don't take stupid risks" guy be correct, and NOT some strawman for secretly evil or always wrong. like startrek, etc. "screw your mission protocols, my hunch will be correct 100% of the time!"