I really don't feel this way. Seemed pretty similar to me, noticeably better, but marginally. What am I missing?

It may depend on your specific workload. E.g. for regular webdev work Opus is more than adequate, for heavy duty data analysis, for experimental stuff and for complex systems it was night and day.

I had only a few places where I did spot a difference but that difference was significant and I can imagine where people would be amazed.

It's interesting, I tried a decent amount of "heavy duty data analysis", and found it pretty similar. But a lot of what I did was about it finding and cobbling together the right things from our existing library of domain specific tooling, which opus is already good at. But perhaps it would have impressed me more if it were starting from zero.

What kind of "experimental stuff and complex systems" did you try that it excelled at?

Nothing. It had marginal gains. People just romanticize it cause it's gone.