On of the most heavily underestimated features in ZDoom are the spark particle objects. They are that easy to implement (just the SPARK thing and some OPEN script in a cycle and that's it) but though, they were used very seldom. But why?
They add such a great special detail to the alround atmosphere of your map, if you place them on broken lights or broken doors. You can put them almost everywhere in your map - as long as you don't work on a Heretic/Hexen map or resources without any technical/electrical stuff in there - in just two simple steps. Additionally you can set up some flickering/randomly blinking lights and maybe also another interactive script (if you shot the terminal/light, it gets broken and sparks!). It's just up to your imagination. (buildtime for simple sparking 3-4 minutes)

Summary: I use the sparks the most time on broken lights, broken doors or broken terminals in addition with some flickering lights and special scripts for the broken objects itself and it really isn't that hard to do!
Extra-Buildtime: "3-15 minutes" (depends on the extra scripts you add for interactivity)
Build-Difficulty: "Low"