Im an a**hole of a critic.
But ill try to be as nice as I can
Its really good for your first sig, mine was literally a render on a black bg.
Just stay away from texts that you would usually use in logos, you want something basic. Maybe a better looking version of a basic text like Arial, or New Times Roman.
Other then that Good job, try a border next time as well it adds some flavvvvourr.
And dont make signatures that big. My personal favourite size, is 400-450 x 100-125
EDIT - Thats halo, 2 not halo 3 xD -