Goodfellas is the cocky, overpraised, over-achieving older sibling to Casino's overshadowed, less successful but more brilliant younger brother.
Casino is bolder, funnier, sharper, as stunning all around. Actually kind of makes Goodfellas look like the test run, Casino being the final form. It's purely excessive in a way Goodfellas isn't. Casino is all downfall, it asks less of an emotional investment too, making its moralless characters seem less like tragic heroes than naturally dying stars, destined to either fade away or implode spectacularly.
Hard not think Scorsese sees himself this as an ode to the death of New Hollywood too. "Turned out to be the last time street guys like us were given anything that valuable again [...] today it looks like Disneyland.
But in the end, I'm still here, and I can still pick winners, and that's that."