Created the first prototype of my anthem last night, its dubstep.
I'm not a dubstep-fan, but I think it falls into the nicer category of dubstep. It sounds fine.
It's not what I'd associate with an anthem, like Matty said, but there's no reason a space civ would mimic human's anthem styles, so I guess it's ok.
It ends very abruptly, you might want to add some kind of fade out or a final note or something like that.
When you go for something purely instrumental, it could also make the anthem more varied and interesting by adding variations between the verses, maybe different instruments (or probably rather effects in dubstep)