I own one of these as well. Not as nice condition as yours though. I actually had the choice at the time between NGS and Mystic at the 2015 UK Pinball Party, and bought this as Mystic was way too easy to achieve everything on before the show had ended.
What keeps this game fresh to play is the level of challenge, harder than any of the digital/VPM versions you'll find (including mine). You'd think rolling the game over would be simple given how heavy it is on the collect bonus saucer, but the flippers are set up to not raise as high as on other old Ballys, making it more difficult to catch and control the ball. Bounce passing is an essential skill here. Fast play when set up well also makes up for the apparent emptiness, and the sound package, for only the second Bally to use a digital sound board after Future Spa, is pretty good. Even so, I recommend three ball play and conservative settings if you don't want to clock it too soon.