Has anyone tried to build a scenario with undead? It would be cool to try to simulate a zombie plague.
What about one based on Star Wars? A Force-based "weapon" (lightning, 0-damage TK throw, etc) could be interesting to script. Thinking a "shared ammo pool" that was drained at different rates per weapon, and automatically recharged whenever not in use, and faster if not moving at all.
Star Trek would be fun, too. Poor Bob the redshirt... I imagine there would be more transporters than usual. You could have a variant of a "repair" level where putting a tribble in the replicator would repel the invading Klingons.
Or how about a sonic screwdriver weapon. Modify cyborgs and s'pht into rolling and flying daleks, respectively.
Okay enough daydreaming for now...