Gooder than good
Is something that is really, really good. Not just good, but gooder. Close to goodest, but not quite goodest. Just gooder. Definitely better than good, so its pretty much in between good and goodest. It is gooder.
If you're working in a science lab, and your lab colleague does something that is quite extraordinary. Then you may quip to say then, "my! that was gooder than good."