On the fly (or auto) ISO....huge deal.
Peace
I'm also going to say changing ISO on the fly with digital cameras. Having shot film now for 30-some years it's very nice to be able to "change films" for every shot. My second choice of the little rangefinder dot in the viewfinder for manual focus confirmation is a distant second.
The big seller for me is tracking AF. Also the reason why I switched from Pentax.
I definitely have to go with digital "film" as the one thing I couldn't live without. Not having to change or purchase film - let alone the cost / time of processing - allows me much more freedom when shooting. The cost of cards now is less than the number of images it can hold in just the cost of film. Even better, when I've saved off the images, I can reuse the card many times! Tied in with that is the ability to immediately review my pix in camera after I've taken them to see if any adjustment is required. RAW is tied in with "digital" too. I love lots of the other features of current cameras, but I lived with manual cameras and a light meter, so I could go back to that...wouldn't want to give up the digital features though...