I don't know much about Kraftwerk, but one of my luckier record-shop moments was to buy
Autobahn when it became a hit in 1974. To me, this is by far their best album, mainly because of the kool beetz and the perfect marriage between the gorgeous swishy electronic effects and the topic of the song. (But, as seems typical of Kraftwerk albums, there are skipable tracks on side 2.)
As well as being the highpoint, Autobahn is also the dividing line in their discography imo. Pre-A'bahn albums are robust and experimental affairs.
Kraftwerk 2 from 1971 and
Ralph and Florian from 1973 have some good rousing tracks, that are abstract in the sense that they're not deliberately conjouring up some vision or mood. Instead, you get some powerful musical workouts (along with the usual weaker moments).
What I've heard of Post A'bahn albums (=very little) has been very disappointing. It seems to me that two things happened to Kraftwerk: one, they got too fixated on the notion that their music should be about machines travelling at speed, so they treated us to an evocation of every European mode of transport there is. And two, which was worse, they seemed to become embarrassed by the forthrightness of their earlier work. Instead of that stark and innovative sound, they began to flip-flop between smooth predictable background music and irritating up-tempo electro-pop.
