Can't say this mash-up ever occurred to me, though, in hindsight, it seems sort of obvious. Four people from four different backgrounds trying to conquer a gauntlet to ensure their future survival. Whether they're up against flying monkeys or zombies, the challenge before them is still epic.
The image above was created for the "Character of the Week" contest on Concept Art and was collected by Super Punch in a much more viewable format. Hardly any of the "Oz" re-imaginings are video game related, but they're all extremely impressive and make me upset that the recent SyFy re-imagining was so terrible.
Here's the full shot of the poster, which really sells the "Left 4 Oz" motif.