Yeah, I have about 15 of their albums. The first 4 were pretty much pre-moog/synthesizers, but so good! Their 3rd album Zeit is so fucking awesome, and creepy. It's a double album.....4 songs only on it. Each around, or over 20 minutes. Atem, the 4th album, starts out with one of the most epic 2 minutes ever recorded. Phaedra, and Rubycon were both the next step, with all the new synth/moog/keyboard technology coming out, and those 2 albums are considered classics, and must own albums in the genre. Cyclone, Stratosfear, and Force Majeure (late 70's) are good strong albums as well. The only problem with Cyclone, is there's actually vocals on it.....and the vocals can be a little on the dry side. But musically, Cyclone is good. It depends on what you're looking for.....
To me, their best era was the early 70's albums.
Ambient moog-driven albums....
Pheadra-
Rubycon
Ricochet ( part improvised live album)
More experimental, but still epic, atmospheric albums....
Alpha Centauri
Zeit (my favorite, it's so dark, brooding and massively epic!)
Atem
The Legend,and Sorcerer soundtrack albums are great as well.
A lot of their early to mid 80's material is hit and miss....some are good, others a little too streamlined for my taste.