I don't know what the cow bells are all about, but definitely get Bergtatt as it's probably the best black metal album ever released. It's more of the folky epic black metal sound, instead of raw evil (which would best fit with Nattens Madrigal). Kveldsjanger is also very organic and Scandinavian in approach, but it is mostly acoustic folk based music. But... in my opinion, Bergtatt is by far the best of the early Ulver work, but they got more consistently awesome once they switched to electronics. Depending on my mood, I will say that either Bergtatt or Themes is the best Ulver album, but Themes, Perdition City, Metamorphasis, Silence Teaches You How to Sing, Silencing the Singing, Lyckantropen Themes, and A Quick Fix of Melancholy all add up to a body of work that is far more inspiring and incredible than early Ulver. But if you abhor almost purely electronic music (especially post-Themes work), then I don't know if you'll like these releases.