Koyaanisqatsi is the only film of the trilogy I will show to non-cinephiles; the long opening sequence in Powaqqatsi tends to put them to sleep. Personally, I might watch that sequence on repeat as part of an art gallery show, but as home cinema it requires a "specific mood", and I'm rarely in it. As for the third film... I have to admit I only saw it once, and it didn't leave much of an impression. I remember lots of stock war footage. It seemed didactic.
Koyaanisqatsi is a visual tone poem, and it can change the way you see the world. It's perfectly balanced between connection and detachment to nature and humanity. Best case scenario, it allows its viewers to feel like alien anthropologists. Nothing like a little defamiliarization to see the the world, and other people, more clearly and with a little more empathy.
Still have not seen Baraka, but mean to correct that one of these days.