My thoughts for improvements:
1. Give us a chance to turn off the reversed flippers at 100 ghosts. I hate it, it is no fun at all.
2. Improve multiballs by introducing individual targets. Especially SFMB: the start phase is ok, then the Scoleris and Slimer should disappear (say after a certain number of Hits) to open the playfield again, next target could be the capture of the ghosts lit at the beginning of SFMB, then a Kind of bonus Phase like a moving single ghost that Must be captured (similar to ST). The game is ghostbusters so let us hunt moving ghosts.
3. my biggest concern is the unbalanced scoring depending on the 2x and 3x playfield multipliers. It is just luck to get and activate them in the right moment (during MB or PKE) and their influence on high scores is significant. A good Game without the use of the multipliers will have no chance for a good scoring. For me the scoring now is just luck.