If you need help with qoth, I can assist you there.
It's all map effects, there is actually very little supporting code. Prototypes were done before the game mode code was even started

... Actually QOTH is even optional, you can use map effects to create pseud-gamemode maps as the logic allows you to create rudimentary state machines, i.e. kill 10 guys and door opens and more spawn once you reach a new trigger. You could even create a sort of time-crisis/arenafight like scenario (where you can move freely) where you fight room by room and get some supplies and cool shit.
I wouldn't worry too much about comparisons, the texture set is quite flexible that allows very different styles to be done without too much trouble, go for something unique!