The most striking visual change from what came before was easily the original Star Wars. Saw it numerous times in various states of consciousness.
The first Indiana Jones was a hoot in a special packed sneak preview that my wife snagged tickets to. Comedies were Animal House and There's Something About Mary, both of which were in packed houses that were roaring. Saw Something About Mary in Rhode Island which added to the atmosphere. Same with seeing the first 2 Godfather movies in Providence, a heavily Italian-American area with a strong mafia presense where/when I grew up. By the same token seeing The Blues Brothers in Chicago when it came out added to the packed house atmosphere.
LOTR, Sin City, and 300 were all pretty inventive, but CGI was pretty established by that point. LOTR had a huge following before it became a film, so interest was intense. Gravity was very good as a visual experience too, but I liked the theme too. Avatar was good for 3D, but it's just OK as a movie. The Hobbit series is just overdone.
As far as original/unique screenwriting and editing, Memento attracted a lot of film buffs. Unique gimmick film, but well done. Put me on to Nolan as did Blood Simple for the Coen Brothers which was a great debut. As far as horror/murder/monster, Psycho, Aliens, Jaws had everyone in packed houses edgy as hell. Psycho was groundbreaking for its time and the women would scream and scream.
There's a lot of powerful films I've seen as opposed to the fun theatre experiences above, but that's another thread.