Sooo... I've just completed my first listen of the black metal trilogy. Bergtatt is amazing, and probably my favourite of the three. Kveldssanger is great as well, some amazing folk, I love the vocals and the instruments here, but it isn't as varied as Bergtatt. Nattens Madrigal is, I suspect, a good album but it is absolutely PAINFUL to listen to. I get why it sounds like that, but I still can't enjoy it, which is a shame, because the music seems to be really, really good.
Overall, I'd say that Bergtatt is now my favourite Ulver album, out of those that I've heard. And while they are all very, very different, I'd rank them like this:
1. Bergtatt
2. Shadows of the Sun
3. Kveldssanger
4. Blood Inside
5. Wars of the Roses
6. Perdition City
7. Nattens Madrigal