I liked features like director commentary and deleted scenes (usually deleted for good reason but still interesting)
One of my first DVD experiences was the original Blade film, and it had an alternate ending available to play.
That blew my mind and was an awesome experience. In the age of dial-up internet it wasn't like you could find and / or watch that online.
A few years ago I hurt one of my shoulders pretty badly, so I could barely move and had to sleep in a sitting / reclined position for almost a week. No keyboards, no computers.
Boy oh boy did that LotR premium extended something-something edition on DVD turn out to be a godsend with the countless hours of behind the scenes footage and interviews, and director's commentary. I watched it all.