The theme has always been a flooded mine operated by prisoners. Before the shootout was added, the scenes were timed to the oar cars arrival in each area. The saw blade disconnected itself and hurled toward you and the lights would go out as it got to the edge (Can you here the saw sound any more?). The dynamite went off and the water rushed in as a strobe light added to the effect (I'm gettin' outa here no matter what!). My favorite part was the canaries. The first canary had a sign to explain that its being alive meant there were no dangerous gases escaping. Further into the mine, a second canary hung upside down from its perch (subtle with no sign of explanation). There were no guards in the mine, and I think the riders were actually supposed to be the ones recruited to help as all the prisoners were attempting to escape the flooded mine. It was a pretty cool ride actually before the laser sounds and digital guns were added.
When the shootout was added, the last scene (the tall scene in the tower) was of some ghostly creatures up high and lasers being shot around overhead. I have no earthly idea what they had to do with the mine, and I suppose they were too close to being in the dark arts for HFE.
One Christmas, early into their opening for the season, the flooded mine was transformed into a candy mine. Prisoners were reclothed in red-and-white or green-and-white stripes and they were supposedly mining candy. Christmas lights and big plastic candies of all kinds (peppermints and ribbons, etc.) were strewn all through the mine, and it really was something for the season.
FM was the first real "amusement" ride for SDC. In that sense it is a history piece. Perhaps someone else has more to add to my narrative here.