So here's a couple of ideas, please write feedback and answer the poll. You can also submit your own ideas in the comment section, thank you!

Futuristic War Theme / World War II Theme
The world as we know it, no longer exists
everything is devasted, destroyed, and left
in ruins. Survive the night by crafting your
own weapons, and keep an eye for intruders.
Don't trust anyone, this is war.

Classic RPG Theme
Classic Roleplay theme with classes, races,
custom items, mobs, etc. Pick your race, and fight
your opposition - bring victory upon your land,
and rule the kingdom!

Space Theme
A unqiue theme, with planets orbitting in a solar
system we could never imagine. Futuristic theme
with space bases and laser weapons. Settle down
on your own planet, or fly to a new one using your
fuel in your Jetpack.

The Grid
You fight in serveral arenas, known as grids, you
fight against the enemy team to destroy their
core. Many gamemodes, in many different grids.
Each kill rewards money, as well as a win.
Maybe MW3 Themed.

Got more ideas? Post 'em all!