In truth, to get a real feel for Vintersorg you should sample the entire album for the best impression, the sound from song to song varies. However, if you're looking for just a few songs this is what I listened to that got me into it:
from Cosmic Genesis: Astral and Arcane, Cosmic Genesis, Ars Memorativa(my personal fav), Om Regnbagen Materialiserades.
After hearing those songs, I got the album, then I bought Odemarkens Son. My fav songs from that one would be: Svaltvinter, Under Norrskenets Fallande Ljusspel, Trollbunden, Pa Landet.
Those are the only 2 that I own right now.