The truth is that with this set of themes it is possible to cheat, just make a 8-bit-style graphics game involving a goat in a quest for magic mushrooms to save the people of her planetoid world. Or anything like that ;)
That said, I like the 8-bit theme. I'd love to make a NES or GB style game, in a week :D
The past theme could have cheated by making a game about a guild of alchemist monkeys trying to make a new state of matter in a medieval space station above the moon.
Using all the themes is not cheating, but starting working on your game before the voting ends because you're using all themes ;)
I was joking anyway (don't do it!).
That said, I like the 8-bit theme. I'd love to make a NES or GB style game, in a week :D