1) English language is a must, dubbed or subbed (preferably the latter)
2) Widescreen
3) As complete a print as possible
4) Everything else.
Everything else is nice, but the first three things are a must. I've seen some cracking dvds on various sites, but if I can't understand the film it's pointless. Widescreen can make or break a subtitled film, and, of course, provides a full view of the action. Furthermore, some dvds clearly use cut prints, which spoils the pace, and sometimes the story, of the film. Nice covers and other options are great and add to the package, but without the first three things they don't really mean much to me. I've got loads of dvds where the screen is in 4:3 format, and two people talking are both offscreen, or scenes make no sense because they're cut. That really takes the biscuit!
english options are important no doubt. i agree its number one for me, a wide print as close to the origonal as possible is how i like it. if a print is glass i will grab it for that reason as well