I love nearly all of Stockhausen's electronic music. It was an LP of Gesang der Jünglinge and Kontakte that had by some miracle found its way to the only local classical music record shop in New Plymouth, NZ, way back in 1966 that completely amazed my young schoolboy mind. I had never heard anything like it, and it excited me in he same way that Bach's 48 Preludes and Fugues, Beethoven's last 3 sonatas, Verdi's Requiem and Schoenberg's Pierrot Lunaire did. Visions of new worlds I had never dreamt of.
I still think those 2 works are remarkable, and beautiful, and they remain fresh every time I hear them. I have suggested to some friends who found them incomprehensible that they need to stop listening to them as what they think is 'music'. Our notions of music have been so heavily conditioned by the one language we hear constantly all around us, of the 12 tone tempered scale, melody, harmony and rhythm. (Even to the birds that system is alien. We only need to listen to how mutated, if not mutilated, birdsong becomes when Messiaen attempts to constrict it into our tempered tonality!) Rather listen to it as great aural landscapes. This cue has been useful to some people, not so much to others.
Other electronic works I love include the epic Hymnen, and so many parts of Licht. The background electronic music of Act II of Dienstag is amazing - terrifying, awesomely beautiful, pulverising. And for all its horror somehow inspires the deepest humanity, a profound abhorrence of the abomination that war is. Mittwochs-Gruss, that seems to me to have a sternness, but a gentleness that has a palliative affect after the devastation of Dienstag. I love the massive circling soundscapes that Stockhausen creates. Here they become enfolding, embracing, comforting, hopeful. Freitags-Gruss is also electronic music and I've only listened to this a couiple of times. It sounds to me very gentle, and quite beautiful.
Cosmic Pulses is also an immensely powerful, over-whelming listening experiencing. (I have to admit I cheat with these electronic pieces that were written for more than 2 channels. My music system has a function that allows an 'artificial' 5-channel separation, and miraculously it creates the effect of the sounds of Cosmic Pulses swirling and swooping around me. How close this is to Stockhausen's original sound movement I have no idea, probably not very faithful, but it certainly shows me how significant the movement in space is to the effectiveness of these works). I don't find the electronic sounds Stockhausen uses in any way problematic, and suspect that there is a kind of 'authenticity' in his use of purely electronic sources. I don't find these sounds any more dated or effete then for instance the sounds of the piano, or the violin, or the flute, which have changed but little over the past 200 years and more.
One thing that is certainly true is that this is not music for 'background' listening. You have to give all your concentration into the music to be able to be taken where it wants to take you.
And then there's the use of live electronics . . . . another extraordinary world again, where once again Stockhausen was a pioneer of genius and has left us with so many wonderful works. LOL - I suspect I have raved enough. I could go on for a very long time.