That's funny, as it was also my first "unsupervised" movie, as I went with a friend I had recently met, to a theatre in Ipswich that was about 10 minutes walk away from the motel we were staying at.
I guess that next level of independence in our childhoods helped make this particular movie more significant in our lives.

When I went to see it, I wasn't expecting anything spectacular, because I didn't even know it existed before my friend asked me about going to see it... and I think I may have been thinking it would just be an extra long regular episode.
Then again, the UK comic story "Target 2006" story may have been here by then (it was out around September in the UK, and the Movie was out here some 4 months after the US), so I may have been prepared for the new characters and setting.
I don't even think I was upset over Prime's death... I do remember that we were both just so amazed at what we had just experienced.