When I first saw Blade Runner I was completely underwhelmed, mind you it was the original Voiceover version. Just goes to show even I can be wrong from time to time.
Interesting you mention Dune. I loved that film and was only thinking the other day I'd like to watch it again.
There's a 3 hour long version which David Lynch wanted nothing to do with, (The Alan Smithee versio it's worth a watch though.