Nice cherry picking
Star Wars, Close Encounters, and Aliens are three of the truly great sci-fi films of all time. They defined various aspects of the genre and I will agree that we have not seen truly seminal films like that very much lately. But, we have had plenty of quality in the sci-fi/action genre in recent years. Inception, Avatar, Looper, Edge of Tomorrow, and Dawn of the Apes were all pure sci-fi and are each outstanding films. We are obviously in the golden age of comic book movies with stuff like Avengers and Dark Knight setting a high bar and many films coming close to them in terms of comic book movie quality.
I am not saying we are at the level we were in the late 70s/early 80s, which also brought us Blade Runner and The Thing, but it is not like nothing good is coming out of Hollywood. I somewhat lament the lack of anything truly original from anyone not named Christopher Nolan but we are getting more than enough high quality stuff -- even the stuff based on graphic novels or comic books -- so that I am quite happy.
-Jason "notice I didn't even talk about the early 2000s which gave us the Lord of the Rings trilogy and the first batch of X-Men films... some high quality stuff there!" Evans