Noob question… what’s weird about Ornette Coleman?

So, I am sincerely trying to learn to appreciate jazz. I was surprised when I first listened to Ornette Coleman, because it was… well, less weird than I thought it would be. “Free jazz”, you say? I was expecting shrieking John Zorn or something, but it’s not that at all. It’s melodic, it swings, it even sounds, to me, approachable. To be perfectly honest, it doesn’t sound that different to me from other varieties of “straight ahead” jazz.

What am I missing? Is it to do with the song structure, above all? And as a second question, does that mean that people listening to more traditional standards-based jazz “have” the song structure in their heads as they’re listening, and the more conservative of those people consider song structure so fundamental that they were like “yo, hold up Ornette, that’s not how it’s done…”?

I seem to remember reading somewhere about a “backlash” to Ornette’s music. Why? I feel like I could improve my listening skills if I had some help on these questions.