The first two releases (John Woo films) introduced me to a great filmmaker -- and the many supplements on the two sets gave me a solid and in-depth introduction to Hong Kong cinema.
The box set release of Brazil defined for me what a special edition could and should be.
I still have all three sets and watch them every now and then.
And, OMG, their recent release of the Zatoichi films is simply amazing -- I am saving up the pennies for an eventual purchase.
In the case of "Badlands" and "The Gambler," what stands out for me, besides the gorgeous images, is the prominent use of music by Carl Orff in the first and Gustav Mahler in the second. I've long had both movies on DVD and keep vacillating about buying "Badlands" on Blu-ray, putting it in my Amazon shopping cart and then moving it down to saved for later, because I don't need another Blu-ray I'll watch only once, which it would probably be. And in the case of "The Gambler," it's so depressing watching the self-destructive character played by James Caan that the last time I watched it I ended up yelling at the screen and drowning out the Mahler, so I've never even considered buying that one on Blu-ray -- if I need to hear Mahler, I'll put on one of my SACDs! (A favorite is Leonard Bernstein's original Mahler 1st in just 2-channel stereo with his New York Philharmonic.)