Great Adventure is a theme park in Jackson Township, New Jersey that opened in 1974 and still is open today.
The commercial below was televised in 1975 about a year after the park opened. It was not yet owned by Six Flags.
The ride I remember most is Rolling Thunder, a wooden rollercoaster that operated from 1979-2013. It was a sad day when it closed and was finally demolished. Rolling Thunder was so famous it even has its own Wikipedia page.
I wasn't fond of roller coasters than turned upside down which is why I preferred Rolling Thunder to Lightnin' Loops.
I do remember how Rolling Thunder would s-l-o-w-l-y climb up the tracks and poise for a breathless moment on top -- and then go racing down!
Here is a commercial for the new Rolling Thunder roller coaster in 1979!