Maybe some more textures would be needed to have a well made snow level. There are very few for a well-made level IMHO.
I can take inspiration from UT series, there are great snow levels there. (
DmTundra from Unreal;
AS-Overlord and
DM-Zeto from UT;
DM-Flux2 from UT2003/4;
ONS-Dria from UT2004 and
WAR-ColdHarbor and
DM-KBarge from UT3 for example)
Also, a shader which resembles falling snow flakes can be nice as well.