and then their choices are terrible.Such as 1954's Them! not on the list while 1951's The Thing from Another World at 67 and The Day the Earth Stood Still at 31. These three should be in the top five, not for their special effects but for their plots and believability that survived across the 60 plus years since they were produced.
Today's sci-fi films are 99.9% special effects, .01% plot and no believability as the target audience are 10 to 14 year old boys & girls (and many of today's grown men & women with the same maturity level) who will come back to see the film over and over and over.
Some days I almost wish... 
Helen had never said "Klaatu barada nikto" to Gort--