Re: What was your first time listening to Free Jazz by Ornette Coleman like?
With Merzbow it's just a case of dipping toes until you find something you can stand. He tends to just make music and then release it, there's no 'quality-control' button with his mindset, so to recommend anything specific is difficult. I've listened to a lot of Merzbow but I've barely scratched the surface. Probably the most famous record is '1930' and that's probably as good a place to start as anywhere.
Broadly speaking, the big shift in his style occurred around the early 90s when he shifted from analogue to digital. Anything before then tends to be a little less aggressive and anything after can be very, very harsh. 'Rising Sun' is a particularly aggressive piece that I used to listen to regularly but is hard to get hold of because it was only ever released as a limited edition - I just used to have access to a fantastic library at my old University that was full of odd records and CDs.
'Sphere' is a record that has some actual, repeating patterns. 'Yaho-Niwa' varies a few things and has some softer tracks and some really harsh ones.
My obsession started during my Undergraduate Degree when a lecturer I conversed with regularly suggested that I might quite like the aesthetics behind what he was doing. I think I was the only person on the degree that wrote noise and I ended up composing computer-controlled Onkyokei. My favourite Onkyo record is 'Foldings' by a group of guys led by Tetuzi Akiyama but that's a different story.