Personally, The Rocky Horror Picture Show.
I knew it was going to be quite the experience before I went for the first time‡ but it was so much fun I had to keep going back bringing friends each time.
It's still a fun tradition to do though we haven't done it since last year, we're probably going to try and go again in a few weeks.
‡ I had seen it many times before going to see it in theaters for the first time.
The marketing was incredible because it leaned heavily into "What is the Matrix?" and didn't spoil the plot. It made the movie itself amazing, because you had no idea what to expect.
I cringe just thinking about how that movie would be marketed today. The trailer would probably start off with all the action scenes voiced over by Morpheus explaining exactly what the Matrix was, followed by Agent Smith monologuing about how humans are a virus that needs to be wiped out.
Yes yes 1000 times yes. It was so incredible and there were so many great lines in the film talking about what the Matrix was without actually revealing the mystery. "The matrix is all around you" etc.
Absolute master class in building hype for a movie and as you say, puts modern marketing campaigns absolutely to shame. Although to be fair they did have solid gold to work with.