For me, Gladiator comes to mind. I didn't hate it when I saw it theatrically, but I also didn't really feel all that wowed by it either. Now, I see the utter brilliance in that movie, and rank it third best from Ridley Scott (a lot of bias on my part toward his science fiction masterpieces, Alien and Blade Runner).
Someone mentioned Interstellar. When I saw that one, I absolutely loved it upon walking out of the auditorium. The problem was, the theater I saw it at has one of those bars in it where they had a TV, upon which was playing Texas A&M @ Auburn (2014). I had decided to go to the movie that day because for the second time in my life, I was absolutely certain that A&M was coming no where near the third-ranked team in the nation and would get *****-slapped (the only other time I had this feeling was December '84 when the Ags went in to Austin and beat the hell out of the sips 37-12). When I saw the score on that little TV, I IMMEDIATELY forgot everything about the movie I'd just watched. I mean, it was as if someone pushed a delete button in my memory. And of course, the Ags went on to beat the Tigers that day, so all I could think of was just how fantastic and unexpected that win was. It wasn't until I got the bluray of Interstellar that I remembered how great that movie was.
Someone else mentioned The Thing. I concur with the opinion presented - it was awesome then, and remains awesome now. John Carpenter did in fact have a strong stretch of fantastic movies starting with Halloween and ending with Big Trouble in Little China; after Little China, the quality of his movies took a noticable dip down. But The Fog, Escape From New York, and The Thing along with those other two are all superb movies, and three of those are typically on my watch list for this time of the year. (And it's easy to overlook that JC also made Christine and Starman during that time period).
