Quick look is more than just a preview, it's really a read-only view of the document. You can read entire documents and PDFs, view HTML files rendered, pan through CSVs, etc
I love that you can preview videos in their icons. Where "preview" actually means "watch the entire thing from start to finish".
Yes, there are plugins for the preview pane and some are built-in. That’s very nice, but I prefer having the ability to hit space to preview because of 15 years of muscle memory doing that with macOS.