OK.  The PCE Retrocade Pac Man clone is turning out badassedly.
However, it needs a theme that is not Pac Man
General idea of each:
Dinosaurs::  You are an egg eating dinosaur.  The pellets are eggs.  The power pills are meat, and the ghosts are raptors who are pissed that you're eating their eggs.
Cat/Mouse: You're a Rat (mice aren't BAMFs like rats), pellets are crumbs of food! power pills are cheese! Ghosts are cats! 
Fish: Kinda like dinosaurs only you're fish... You're a fish, you eat littler fish, the power pills are shrimp, and the ghosts are sharks, who are obviously bigger than you!
These are the ideas so far .  I personally like the dinosaur one.
If you have something suggestion wise, post it here!  Lets see what we get out of this.