It's not what I'd call abstract or dark ambient, but the music is definately very atmospheric and ambient-like and it also has strong melodies and emotions.
Today these artists make mostly rubbish, but to me those albums are some of the best electronic music ever. I enjoyed them immensely and I still enjoy listening now and then. I truly experienced some of my best music moments with these albums. So it's just my personal recommendation.
And it sounds different than today's music, no software, no samples, just analog synths and equipment and I love that sound.