Here's 30 of my all time favorite Sci-Fi films, ranked and separated by category.
Grounded Science Fiction:1. Interstellar
2. Inception
3. Ex Machina
4. Looper
5. Moon
6. The Martian
7. The Thing
8. Jurassic Park
9. Under The Skin
10. Terminator 2
Deep-Tech Sci Fi:1. 2001: A Space Oddysey
2. Blade Runner
3. Sunshine
4. The Matrix
5. Alien
6. Star Trek: First Contact
7. Aliens
8. Edge of Tomorrow
9. Star Trek: The Wrath of Khan
10. Star Trek: Insurrection
Science Fantasy:1. Cloud Atlas
2. Donnie Darko
3. Avatar
4. Star Wars: The Empire Strikes Back
5. Guardians of The Galaxy
6. Star Trek: Beyond
7. Star Wars
8. Star Trek (2009)
9. Star Wars: Return of the Jedi
10. Star Trek: Into Darkness
Upcoming:Valerian and the City of a Thousand Planets (looks pretty bad but I'm still gonna see it).
Dune, whilst not the best SciFi movie by far, it's certainly defining of the genre at the time.
Huh? No, it's actually really mediocre. You might be confusing it for the conceptualized Dune film by Alejandro Jodorowsky.