I have to admit I was fairly dissapointed by Blood Inside. It was the first Ulver album I heard, and it almost turned me off the band. It just seems to me that Ulver tried to experiment too much, and they couldn't pull it off.
Personally, my two favourite records are Bergtatt and Nattrens Madrical. Bergtatt is freaking awesome, so foresty and beautiful, probably my favourite black metal album ever. NM is probably better, just in terms of the sheer art and maybe even beauty, but it's really hard to listen too, what with the production. Still, Nattrens is an absolute masterpiece, just very difficult to listen too. I probably should describe the music- it's insanely fast black metal, with hardly any break.. But it's done really damn well.
I haven't heard too much of their other stuff, but I thought the Metamorphosis EP was a solid slab of techno/trip hop/ambient/whatever. Personally though, I think you should get Bergtatt next (because It's freaking awesome) and then just buy your way through their discography.