Doesn't the title of the list explain it well enough? This is a list of hight quality "short" films. Easy as that.
The quality may differ from person to person, I'm not even a fan of all these films myself. Overall, I think there's more than enough interesting titles here for every man or woman considering themselves a cinephile.
PS: I haven't seen them all myself, so don't come blaming me if they turn out to be bad! ;)
NB! Oh, some of the titles exceed the 90 min limit by two or three minutes, but I've included them anyway!