Jurassic Park - Truly an amazing experience, especially since the special effects still hold up well today.
When the Sta-Puft Marshmallow Man showed up at the end, it was pandemonium. I've never heard a theater laugh like that.
In my lifetime, I think back to these ones:
Jurassic Park- It's the earliest memory I have of going to the cinema to see a movie. Loved dinosaurs as a kid, and this blew my mind.
Spider-Man - CBMs were not a norm at the time, and Spider-Man was a real event when it happened.
The Avengers - Seeing the MCU come together and bring us something that was only ever a pipe dream due to rights situations and such was a dream come true.
These are probably my 3 favorite film going experiences.